Mercurial > vim
annotate runtime/doc/vim9.txt @ 23358:b3142fc0a414 v8.2.2222
patch 8.2.2222: Vim9: cannot keep script variables when reloading
Commit: https://github.com/vim/vim/commit/2b32700dabf392566d8e9fef76e0d587a891ee3e
Author: Bram Moolenaar <Bram@vim.org>
Date: Sat Dec 26 15:39:31 2020 +0100
patch 8.2.2222: Vim9: cannot keep script variables when reloading
Problem: Vim9: cannot keep script variables when reloading.
Solution: Add the "noclear" argument to :vim9script.
author | Bram Moolenaar <Bram@vim.org> |
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date | Sat, 26 Dec 2020 15:45:04 +0100 |
parents | c76240efdf02 |
children | eb7d8f39363c |
rev | line source |
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1 *vim9.txt* For Vim version 8.2. Last change: 2020 Dec 24 |
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2 |
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3 |
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4 VIM REFERENCE MANUAL by Bram Moolenaar |
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5 |
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6 |
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7 THIS IS STILL UNDER DEVELOPMENT - ANYTHING CAN BREAK - ANYTHING CAN CHANGE |
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8 |
23305 | 9 Vim9 script commands and expressions. *Vim9* |
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10 |
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11 Most expression help is in |eval.txt|. This file is about the new syntax and |
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12 features in Vim9 script. |
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13 |
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14 THIS IS STILL UNDER DEVELOPMENT - ANYTHING CAN BREAK - ANYTHING CAN CHANGE |
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15 |
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16 |
21676 | 17 1. What is Vim9 script? |vim9-script| |
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18 2. Differences |vim9-differences| |
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19 3. New style functions |fast-functions| |
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20 4. Types |vim9-types| |
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21 5. Namespace, Import and Export |vim9script| |
22328 | 22 6. Future work: classes |vim9-classes| |
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23 |
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24 9. Rationale |vim9-rationale| |
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25 |
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26 ============================================================================== |
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27 |
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28 1. What is Vim9 script? *Vim9-script* |
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29 |
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30 THIS IS STILL UNDER DEVELOPMENT - ANYTHING CAN BREAK - ANYTHING CAN CHANGE |
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31 |
20241 | 32 Vim script has been growing over time, while preserving backwards |
33 compatibility. That means bad choices from the past often can't be changed | |
20965 | 34 and compatibility with Vi restricts possible solutions. Execution is quite |
20241 | 35 slow, each line is parsed every time it is executed. |
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36 |
20241 | 37 The main goal of Vim9 script is to drastically improve performance. This is |
38 accomplished by compiling commands into instructions that can be efficiently | |
39 executed. An increase in execution speed of 10 to 100 times can be expected. | |
40 | |
41 A secondary goal is to avoid Vim-specific constructs and get closer to | |
42 commonly used programming languages, such as JavaScript, TypeScript and Java. | |
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43 |
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44 The performance improvements can only be achieved by not being 100% backwards |
20552 | 45 compatible. For example, making function arguments available in the |
46 "a:" dictionary adds quite a lot of overhead. In a Vim9 function this | |
47 dictionary is not available. Other differences are more subtle, such as how | |
48 errors are handled. | |
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49 |
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50 The Vim9 script syntax and semantics are used in: |
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51 - a function defined with the `:def` command |
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52 - a script file where the first command is `vim9script` |
22328 | 53 - an autocommand defined in the context of the above |
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54 |
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55 When using `:function` in a Vim9 script file the legacy syntax is used. |
20241 | 56 However, this can be confusing and is therefore discouraged. |
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57 |
20241 | 58 Vim9 script and legacy Vim script can be mixed. There is no requirement to |
22328 | 59 rewrite old scripts, they keep working as before. You may want to use a few |
60 `:def` functions for code that needs to be fast. | |
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61 |
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62 ============================================================================== |
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63 |
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64 2. Differences from legacy Vim script *vim9-differences* |
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65 |
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66 THIS IS STILL UNDER DEVELOPMENT - ANYTHING CAN BREAK - ANYTHING CAN CHANGE |
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67 |
22441 | 68 Overview ~ |
69 | |
70 Brief summary of the differences you will most often encounter when using Vim9 | |
71 script and `:def` functions; details are below: | |
72 - Comments start with #, not ": > | |
73 echo "hello" # comment | |
74 - Using a backslash for line continuation is hardly ever needed: > | |
75 echo "hello " | |
76 .. yourName | |
77 .. ", how are you?" | |
78 - White space is required in many places. | |
79 - Assign values without `:let`, declare variables with `:var`: > | |
80 var count = 0 | |
81 count += 3 | |
82 - Constants can be declared with `:final` and `:const`: > | |
83 final matches = [] # add matches | |
84 const names = ['Betty', 'Peter'] # cannot be changed | |
85 - `:final` cannot be used as an abbreviation of `:finally`. | |
86 - Variables and functions are script-local by default. | |
87 - Functions are declared with argument types and return type: > | |
88 def CallMe(count: number, message: string): bool | |
89 - Call functions without `:call`: > | |
90 writefile(['done'], 'file.txt') | |
91 - You cannot use `:xit`, `:t`, `:append`, `:change`, `:insert` or curly-braces | |
92 names. | |
93 - A range before a command must be prefixed with a colon: > | |
94 :%s/this/that | |
95 | |
96 | |
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97 Comments starting with # ~ |
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98 |
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99 In legacy Vim script comments start with double quote. In Vim9 script |
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100 comments start with #. > |
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101 # declarations |
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102 var count = 0 # number of occurrences |
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103 |
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104 The reason is that a double quote can also be the start of a string. In many |
21825 | 105 places, especially halfway through an expression with a line break, it's hard |
106 to tell what the meaning is, since both a string and a comment can be followed | |
107 by arbitrary text. To avoid confusion only # comments are recognized. This | |
108 is the same as in shell scripts and Python programs. | |
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109 |
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110 In Vi # is a command to list text with numbers. In Vim9 script you can use |
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111 `:number` for that. > |
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112 101 number |
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113 |
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114 To improve readability there must be a space between a command and the # |
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115 that starts a comment: > |
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116 var = value # comment |
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117 var = value# error! |
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118 |
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119 In legacy script # is also used for the alternate file name. In Vim9 script |
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120 you need to use %% instead. Instead of ## use %%% (stands for all arguments). |
20115 | 121 |
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122 |
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123 Vim9 functions ~ |
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124 |
20241 | 125 A function defined with `:def` is compiled. Execution is many times faster, |
126 often 10x to 100x times. | |
127 | |
20552 | 128 Many errors are already found when compiling, before the function is executed. |
20241 | 129 The syntax is strict, to enforce code that is easy to read and understand. |
130 | |
23164 | 131 Compilation is done when either of these is encountered: |
132 - the first time the function is called | |
21991 | 133 - when the `:defcompile` command is encountered in the script where the |
134 function was defined | |
135 - `:disassemble` is used for the function. | |
136 - a function that is compiled calls the function or uses it as a function | |
137 reference | |
20552 | 138 |
139 `:def` has no options like `:function` does: "range", "abort", "dict" or | |
23164 | 140 "closure". A `:def` function always aborts on an error (unless `:silent!` was |
141 used for the command or inside a `:try` block), does not get a range passed | |
23305 | 142 cannot be a "dict" function, and can always be a closure. |
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143 |
20241 | 144 The argument types and return type need to be specified. The "any" type can |
145 be used, type checking will then be done at runtime, like with legacy | |
146 functions. | |
147 | |
21825 | 148 Arguments are accessed by name, without "a:", just like any other language. |
149 There is no "a:" dictionary or "a:000" list. | |
20241 | 150 |
151 Variable arguments are defined as the last argument, with a name and have a | |
21825 | 152 list type, similar to TypeScript. For example, a list of numbers: > |
22171 | 153 def MyFunc(...itemlist: list<number>) |
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154 for item in itemlist |
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155 ... |
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156 |
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157 |
20241 | 158 Functions and variables are script-local by default ~ |
20856 | 159 *vim9-scopes* |
20115 | 160 When using `:function` or `:def` to specify a new function at the script level |
161 in a Vim9 script, the function is local to the script, as if "s:" was | |
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162 prefixed. Using the "s:" prefix is optional. To define a global function or |
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163 variable the "g:" prefix must be used. For functions in an autoload script |
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164 the "name#" prefix is sufficient. > |
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165 def ThisFunction() # script-local |
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166 def s:ThisFunction() # script-local |
22171 | 167 def g:ThatFunction() # global |
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168 def scriptname#function() # autoload |
20115 | 169 |
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170 When using `:function` or `:def` to specify a nested function inside a `:def` |
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171 function, this nested function is local to the code block it is defined in. |
22565 | 172 In a `:def` function it is not possible to define a script-local function. It |
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173 is possible to define a global function by using the "g:" prefix. |
20115 | 174 |
175 When referring to a function and no "s:" or "g:" prefix is used, Vim will | |
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176 search for the function: |
22565 | 177 - in the function scope, in block scopes |
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178 - in the script scope, possibly imported |
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179 - in the list of global functions |
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180 However, it is recommended to always use "g:" to refer to a global function |
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181 for clarity. |
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182 |
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183 In all cases the function must be defined before used. That is when it is |
22723 | 184 called, when `:defcompile` causes it to be compiled, or when code that calls |
185 it is being compiled (to figure out the return type). | |
20241 | 186 |
21676 | 187 The result is that functions and variables without a namespace can usually be |
20241 | 188 found in the script, either defined there or imported. Global functions and |
21676 | 189 variables could be defined anywhere (good luck finding out where!). |
20115 | 190 |
21825 | 191 Global functions can still be defined and deleted at nearly any time. In |
20317 | 192 Vim9 script script-local functions are defined once when the script is sourced |
20552 | 193 and cannot be deleted or replaced. |
20115 | 194 |
23305 | 195 When compiling a function and a function call is encountered for a function |
196 that is not (yet) defined, the |FuncUndefined| autocommand is not triggered. | |
197 You can use an autoload function if needed, or call a legacy function and have | |
198 |FuncUndefined| triggered there. | |
199 | |
20115 | 200 |
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201 Reloading a Vim9 script clears functions and variables by default ~ |
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202 *vim9-reload* |
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203 When loading a legacy Vim script a second time nothing is removed, the |
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204 commands will replace existing variables and functions and create new ones. |
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205 |
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206 When loading a Vim9 script a second time all existing script-local functions |
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207 and variables are deleted, thus you start with a clean slate. This is useful |
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208 if you are developing a plugin and want to try a new version. If you renamed |
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209 something you don't have to worry about the old name still hanging around. |
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210 |
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211 If you do want to keep items, use: > |
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212 vimscript noclear |
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213 |
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214 You want to use this in scripts that use a `finish` command to bail out at |
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215 some point when loaded again. E.g. when a buffer local option is set: > |
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216 vimscript noclear |
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217 setlocal completefunc=SomeFunc |
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218 if exists('*SomeFunc') | finish | endif |
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219 def g:SomeFunc() |
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220 .... |
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221 |
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222 There is one gotcha: If a compiled function is replaced and it is called from |
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223 another compiled function that is not replaced, it will try to call the |
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224 function from before it was replaced, which no longer exists. This doesn't |
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225 work: > |
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226 vimscript noclear |
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227 |
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228 def ReplaceMe() |
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229 echo 'function redefined every time' |
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230 enddef |
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231 |
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232 if exists('s:loaded') | finish | endif |
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233 var s:loaded = true |
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234 |
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235 def NotReplaced() |
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236 ReplaceMe() # Error if ReplaceMe() was redefined |
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237 enddef |
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238 |
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239 |
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240 Variable declarations with :var, :final and :const ~ |
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241 *vim9-declaration* *:var* |
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242 Local variables need to be declared with `:var`. Local constants need to be |
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243 declared with `:final` or `:const`. We refer to both as "variables" in this |
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244 section. |
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245 |
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246 Variables can be local to a script, function or code block: > |
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247 vim9script |
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248 var script_var = 123 |
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249 def SomeFunc() |
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250 var func_var = script_var |
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251 if cond |
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252 var block_var = func_var |
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253 ... |
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254 |
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255 The variables are only visible in the block where they are defined and nested |
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256 blocks. Once the block ends the variable is no longer accessible: > |
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257 if cond |
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258 var inner = 5 |
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259 else |
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260 var inner = 0 |
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261 endif |
22171 | 262 echo inner # Error! |
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263 |
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264 The declaration must be done earlier: > |
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265 var inner: number |
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266 if cond |
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267 inner = 5 |
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268 else |
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269 inner = 0 |
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270 endif |
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271 echo inner |
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272 |
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273 To intentionally hide a variable from code that follows, a block can be |
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274 used: > |
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275 { |
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276 var temp = 'temp' |
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277 ... |
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278 } |
22171 | 279 echo temp # Error! |
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280 |
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281 Declaring a variable with a type but without an initializer will initialize to |
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282 zero, false or empty. |
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283 |
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284 In Vim9 script `:let` cannot be used. An existing variable is assigned to |
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285 without any command. The same for global, window, tab, buffer and Vim |
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286 variables, because they are not really declared. They can also be deleted |
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287 with `:unlet`. |
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288 |
21676 | 289 Variables and functions cannot shadow previously defined or imported variables |
290 and functions. | |
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291 Variables may shadow Ex commands, rename the variable if needed. |
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292 |
20241 | 293 Global variables and user defined functions must be prefixed with "g:", also |
294 at the script level. > | |
19968 | 295 vim9script |
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296 var script_local = 'text' |
21499 | 297 g:global = 'value' |
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298 var Funcref = g:ThatFunction |
19968 | 299 |
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300 Since `&opt = value` is now assigning a value to option "opt", ":&" cannot be |
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301 used to repeat a `:substitute` command. |
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302 |
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303 |
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304 Constants ~ |
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305 *vim9-const* *vim9-final* |
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306 How constants work varies between languages. Some consider a variable that |
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307 can't be assigned another value a constant. JavaScript is an example. Others |
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308 also make the value immutable, thus when a constant uses a list, the list |
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309 cannot be changed. In Vim9 we can use both. |
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310 |
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311 `:const` is used for making both the variable and the value a constant. Use |
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312 this for composite structures that you want to make sure will not be modified. |
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313 Example: > |
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314 const myList = [1, 2] |
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315 myList = [3, 4] # Error! |
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316 myList[0] = 9 # Error! |
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317 muList->add(3) # Error! |
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318 < *:final* |
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319 `:final` is used for making only the variable a constant, the value can be |
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320 changed. This is well known from Java. Example: > |
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321 final myList = [1, 2] |
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322 myList = [3, 4] # Error! |
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323 myList[0] = 9 # OK |
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324 muList->add(3) # OK |
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325 |
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326 It is common to write constants as ALL_CAPS, but you don't have to. |
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327 |
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328 The constant only applies to the value itself, not what it refers to. > |
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329 final females = ["Mary"] |
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330 const NAMES = [["John", "Peter"], females] |
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331 NAMES[0] = ["Jack"] # Error! |
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332 NAMES[0][0] = "Jack" # Error! |
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333 NAMES[1] = ["Emma"] # Error! |
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334 Names[1][0] = "Emma" # OK, now females[0] == "Emma" |
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335 |
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336 < *E1092* |
21499 | 337 Declaring more than one variable at a time, using the unpack notation, is |
338 currently not supported: > | |
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339 var [v1, v2] = GetValues() # Error! |
21499 | 340 That is because the type needs to be inferred from the list item type, which |
341 isn't that easy. | |
342 | |
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343 |
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344 Omitting :call and :eval ~ |
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345 |
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346 Functions can be called without `:call`: > |
22171 | 347 writefile(lines, 'file') |
19303 | 348 Using `:call` is still possible, but this is discouraged. |
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349 |
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350 A method call without `eval` is possible, so long as the start is an |
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351 identifier or can't be an Ex command. Examples: > |
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352 myList->add(123) |
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353 g:myList->add(123) |
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354 [1, 2, 3]->Process() |
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355 {a: 1, b: 2}->Process() |
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356 "foobar"->Process() |
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357 ("foobar")->Process() |
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358 'foobar'->Process() |
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359 ('foobar')->Process() |
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360 |
21825 | 361 In the rare case there is ambiguity between a function name and an Ex command, |
21676 | 362 prepend ":" to make clear you want to use the Ex command. For example, there |
363 is both the `:substitute` command and the `substitute()` function. When the | |
364 line starts with `substitute(` this will use the function. Prepend a colon to | |
365 use the command instead: > | |
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366 :substitute(pattern (replacement ( |
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367 |
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368 Note that while variables need to be defined before they can be used, |
21825 | 369 functions can be called before being defined. This is required to allow |
370 for cyclic dependencies between functions. It is slightly less efficient, | |
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371 since the function has to be looked up by name. And a typo in the function |
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372 name will only be found when the function is called. |
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373 |
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374 |
19968 | 375 Omitting function() ~ |
376 | |
377 A user defined function can be used as a function reference in an expression | |
378 without `function()`. The argument types and return type will then be checked. | |
379 The function must already have been defined. > | |
380 | |
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381 var Funcref = MyFunction |
19968 | 382 |
383 When using `function()` the resulting type is "func", a function with any | |
384 number of arguments and any return type. The function can be defined later. | |
385 | |
386 | |
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387 Lambda using => instead of -> ~ |
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388 |
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389 In legacy script there can be confusion between using "->" for a method call |
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390 and for a lambda. Also, when a "{" is found the parser needs to figure out if |
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391 it is the start of a lambda or a dictionary, which is now more complicated |
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392 because of the use of argument types. |
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393 |
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394 To avoid these problems Vim9 script uses a different syntax for a lambda, |
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395 which is similar to Javascript: > |
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396 var Lambda = (arg) => expression |
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397 |
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398 No line break is allowed in the arguments of a lambda up to and including the |
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399 "=>". This is OK: > |
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400 filter(list, (k, v) => |
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401 v > 0) |
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402 This does not work: > |
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403 filter(list, (k, v) |
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404 => v > 0) |
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405 This also does not work: |
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406 filter(list, (k, |
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407 v) => v > 0) |
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408 |
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409 Additionally, a lambda can contain statements in {}: > |
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410 var Lambda = (arg) => { |
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411 g:was_called = 'yes' |
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412 return expression |
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413 } |
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414 NOT IMPLEMENTED YET |
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415 |
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416 To avoid the "{" of a dictionary literal to be recognized as a statement block |
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417 wrap it in parenthesis: > |
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418 var Lambda = (arg) => ({key: 42}) |
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419 |
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420 |
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421 Automatic line continuation ~ |
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422 |
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423 In many cases it is obvious that an expression continues on the next line. In |
21676 | 424 those cases there is no need to prefix the line with a backslash |
425 |line-continuation|. For example, when a list spans multiple lines: > | |
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426 var mylist = [ |
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427 'one', |
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428 'two', |
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429 ] |
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430 And when a dict spans multiple lines: > |
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431 var mydict = { |
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432 one: 1, |
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433 two: 2, |
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434 } |
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435 Function call: > |
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436 var result = Func( |
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437 arg1, |
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438 arg2 |
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439 ) |
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440 |
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441 For binary operators in expressions not in [], {} or () a line break is |
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442 possible just before or after the operator. For example: > |
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443 var text = lead |
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444 .. middle |
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445 .. end |
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446 var total = start + |
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447 end - |
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448 correction |
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449 var result = positive |
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450 ? PosFunc(arg) |
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451 : NegFunc(arg) |
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452 |
21499 | 453 For a method call using "->" and a member using a dot, a line break is allowed |
454 before it: > | |
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455 var result = GetBuilder() |
20965 | 456 ->BuilderSetWidth(333) |
457 ->BuilderSetHeight(777) | |
458 ->BuilderBuild() | |
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459 var result = MyDict |
21499 | 460 .member |
20965 | 461 |
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462 < *E1050* |
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463 To make it possible for the operator at the start of the line to be |
21250 | 464 recognized, it is required to put a colon before a range. This will add |
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465 "start" and print: > |
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466 var result = start |
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467 + print |
21250 | 468 Like this: > |
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469 var result = start + print |
21250 | 470 |
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471 This will assign "start" and print a line: > |
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472 var result = start |
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473 :+ print |
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474 |
23047 | 475 Note that the colon is not required for the |+cmd| argument: > |
476 edit +6 fname | |
477 | |
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478 It is also possible to split a function header over multiple lines, in between |
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479 arguments: > |
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480 def MyFunc( |
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481 text: string, |
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482 separator = '-' |
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483 ): string |
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484 |
23305 | 485 Since a continuation line cannot be easily recognized the parsing of commands |
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486 has been made stricter. E.g., because of the error in the first line, the |
23305 | 487 second line is seen as a separate command: > |
488 popup_create(some invalid expression, { | |
489 exit_cb: Func}) | |
490 Now "exit_cb: Func})" is actually a valid command: save any changes to the | |
491 file "_cb: Func})" and exit. To avoid this kind of mistake in Vim9 script | |
492 there must be white space between most command names and the argument. | |
493 | |
494 | |
21250 | 495 Notes: |
496 - "enddef" cannot be used at the start of a continuation line, it ends the | |
497 current function. | |
498 - No line break is allowed in the LHS of an assignment. Specifically when | |
499 unpacking a list |:let-unpack|. This is OK: > | |
22171 | 500 [var1, var2] = |
21250 | 501 Func() |
502 < This does not work: > | |
22171 | 503 [var1, |
21250 | 504 var2] = |
505 Func() | |
506 - No line break is allowed in between arguments of an `:echo`, `:execute` and | |
507 similar commands. This is OK: > | |
22171 | 508 echo [1, |
21250 | 509 2] [3, |
510 4] | |
511 < This does not work: > | |
22171 | 512 echo [1, 2] |
21250 | 513 [3, 4] |
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514 |
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515 No curly braces expansion ~ |
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516 |
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517 |curly-braces-names| cannot be used. |
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518 |
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519 |
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520 Dictionary literals ~ |
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521 |
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522 Traditionally Vim has supported dictionary literals with a {} syntax: > |
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523 let dict = {'key': value} |
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524 |
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525 Later it became clear that using a simple text key is very common, thus |
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526 literal dictionaries were introduced in a backwards compatible way: > |
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527 let dict = #{key: value} |
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528 |
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529 However, this #{} syntax is unlike any existing language. As it turns out |
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530 that using a literal key is much more common than using an expression, and |
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531 considering that JavaScript uses this syntax, using the {} form for dictionary |
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532 literals is considered a much more useful syntax. In Vim9 script the {} form |
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533 uses literal keys: > |
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534 let dict = {key: value} |
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535 |
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536 This works for alphanumeric characters, underscore and dash. If you want to |
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537 use another character, use a single or double quoted string: > |
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538 let dict = {'key with space': value} |
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539 let dict = {"key\twith\ttabs": value} |
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540 let dict = {'': value} # empty key |
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541 |
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542 In case the key needs to be an expression, square brackets can be used, just |
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543 like in JavaScript: > |
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544 let dict = {["key" .. nr]: value} |
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545 |
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546 |
21584
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547 No :xit, :t, :append, :change or :insert ~ |
19303 | 548 |
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549 These commands are too easily confused with local variable names. |
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550 Instead of `:x` or `:xit` you can use `:exit`. |
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551 Instead of `:t` you can use `:copy`. |
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552 |
19303 | 553 |
554 Comparators ~ | |
555 | |
556 The 'ignorecase' option is not used for comparators that use strings. | |
19181
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557 |
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558 |
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559 White space ~ |
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560 |
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561 Vim9 script enforces proper use of white space. This is no longer allowed: > |
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562 var name=234 # Error! |
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563 var name= 234 # Error! |
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564 var name =234 # Error! |
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565 There must be white space before and after the "=": > |
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566 var name = 234 # OK |
21250 | 567 White space must also be put before the # that starts a comment after a |
568 command: > | |
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569 var name = 234# Error! |
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570 var name = 234 # OK |
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571 |
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572 White space is required around most operators. |
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573 |
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574 White space is not allowed: |
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575 - Between a function name and the "(": > |
22171 | 576 call Func (arg) # Error! |
577 call Func | |
578 \ (arg) # Error! | |
579 call Func(arg) # OK | |
580 call Func( | |
581 \ arg) # OK | |
582 call Func( | |
583 \ arg # OK | |
19473
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patch 8.2.0294: cannot use Ex command that is also a function name
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584 \ ) |
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585 |
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586 |
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587 Conditions and expressions ~ |
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588 |
22500
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patch 8.2.1798: Vim9: trinary operator condition is too permissive
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589 Conditions and expressions are mostly working like they do in other languages. |
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590 Some values are different from legacy Vim script: |
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591 value legacy Vim script Vim9 script ~ |
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592 0 falsy falsy |
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593 1 truthy truthy |
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594 99 truthy Error! |
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595 "0" falsy Error! |
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596 "99" truthy Error! |
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597 "text" falsy Error! |
19181
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598 |
22500
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599 For the "??" operator and when using "!" then there is no error, every value |
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600 is either falsy or truthy. This is mostly like JavaScript, except that an |
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601 empty list and dict is falsy: |
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602 |
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603 type truthy when ~ |
22272
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604 bool v:true or 1 |
19181
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605 number non-zero |
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606 float non-zero |
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607 string non-empty |
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608 blob non-empty |
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609 list non-empty (different from JavaScript) |
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610 dictionary non-empty (different from JavaScript) |
19968 | 611 func when there is a function name |
19181
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612 special v:true |
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613 job when not NULL |
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614 channel when not NULL |
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615 class when not NULL |
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616 object when not NULL (TODO: when isTrue() returns v:true) |
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617 |
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618 The boolean operators "||" and "&&" expect the values to be boolean, zero or |
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|
619 one: > |
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620 1 || false == true |
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621 0 || 1 == true |
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622 0 || false == false |
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623 1 && true == true |
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624 0 && 1 == false |
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625 8 || 0 Error! |
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626 'yes' && 0 Error! |
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627 [] || 99 Error! |
19181
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628 |
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629 When using "!" for inverting, there is no error for using any type and the |
22500
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630 result is a boolean. "!!" can be used to turn any value into boolean: > |
22494
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631 !'yes' == false |
22500
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632 !![] == false |
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633 !![1, 2, 3] == true |
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634 |
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635 When using "`.."` for string concatenation arguments of simple types are |
22500
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636 always converted to string: > |
19181
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637 'hello ' .. 123 == 'hello 123' |
21825 | 638 'hello ' .. v:true == 'hello v:true' |
19181
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639 |
21771
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|
640 Simple types are string, float, special and bool. For other types |string()| |
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641 can be used. |
22171 | 642 *false* *true* |
19181
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643 In Vim9 script one can use "true" for v:true and "false" for v:false. |
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644 |
21825 | 645 Indexing a string with [idx] or [idx, idx] uses character indexes instead of |
646 byte indexes. Example: > | |
647 echo 'bár'[1] | |
648 In legacy script this results in the character 0xc3 (an illegal byte), in Vim9 | |
649 script this results in the string 'á'. | |
650 | |
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651 |
21093 | 652 What to watch out for ~ |
653 *vim9-gotchas* | |
654 Vim9 was designed to be closer to often used programming languages, but at the | |
655 same time tries to support the legacy Vim commands. Some compromises had to | |
656 be made. Here is a summary of what might be unexpected. | |
657 | |
658 Ex command ranges need to be prefixed with a colon. > | |
22171 | 659 -> # legacy Vim: shifts the previous line to the right |
660 ->func() # Vim9: method call in continuation line | |
661 :-> # Vim9: shifts the previous line to the right | |
21093 | 662 |
22171 | 663 %s/a/b # legacy Vim: substitute on all lines |
21093 | 664 x = alongname |
22171 | 665 % another # Vim9: line continuation without a backslash |
666 :%s/a/b # Vim9: substitute on all lines | |
667 'text'->func() # Vim9: method call | |
668 :'t # legacy Vim: jump to mark m | |
21093 | 669 |
21676 | 670 Some Ex commands can be confused with assignments in Vim9 script: > |
671 g:name = value # assignment | |
672 g:pattern:cmd # invalid command - ERROR | |
673 :g:pattern:cmd # :global command | |
674 | |
21093 | 675 Functions defined with `:def` compile the whole function. Legacy functions |
676 can bail out, and the following lines are not parsed: > | |
677 func Maybe() | |
678 if !has('feature') | |
679 return | |
680 endif | |
681 use-feature | |
682 endfunc | |
683 Vim9 functions are compiled as a whole: > | |
684 def Maybe() | |
685 if !has('feature') | |
686 return | |
687 endif | |
22171 | 688 use-feature # May give compilation error |
21093 | 689 enddef |
690 For a workaround, split it in two functions: > | |
691 func Maybe() | |
692 if has('feature') | |
693 call MaybyInner() | |
694 endif | |
695 endfunc | |
696 if has('feature') | |
697 def MaybeInner() | |
698 use-feature | |
699 enddef | |
700 endif | |
22171 | 701 Or put the unsupported code inside an `if` with a constant expression that |
21991 | 702 evaluates to false: > |
703 def Maybe() | |
704 if has('feature') | |
705 use-feature | |
706 endif | |
707 enddef | |
708 Note that for unrecognized commands there is no check for "|" and a following | |
709 command. This will give an error for missing `endif`: > | |
710 def Maybe() | |
711 if has('feature') | use-feature | endif | |
712 enddef | |
21093 | 713 |
23305 | 714 Other differences ~ |
715 | |
716 Patterns are used like 'magic' is set, unless explicitly overruled. | |
717 The 'edcompatible' option value is not used. | |
718 The 'gdefault' option value is not used. | |
719 | |
720 | |
19181
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721 ============================================================================== |
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722 |
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723 3. New style functions *fast-functions* |
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724 |
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725 THIS IS STILL UNDER DEVELOPMENT - ANYTHING CAN BREAK - ANYTHING CAN CHANGE |
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726 |
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727 *:def* |
21825 | 728 :def[!] {name}([arguments])[: {return-type}] |
19181
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729 Define a new function by the name {name}. The body of |
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730 the function follows in the next lines, until the |
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731 matching `:enddef`. |
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732 |
19904
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|
733 When {return-type} is omitted or is "void" the |
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|
734 function is not expected to return anything. |
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735 |
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736 {arguments} is a sequence of zero or more argument |
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737 declarations. There are three forms: |
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738 {name}: {type} |
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739 {name} = {value} |
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740 {name}: {type} = {value} |
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741 The first form is a mandatory argument, the caller |
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742 must always provide them. |
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743 The second and third form are optional arguments. |
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744 When the caller omits an argument the {value} is used. |
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745 |
20856 | 746 The function will be compiled into instructions when |
21499 | 747 called, or when `:disassemble` or `:defcompile` is |
748 used. Syntax and type errors will be produced at that | |
749 time. | |
20856 | 750 |
21499 | 751 It is possible to nest `:def` inside another `:def` or |
752 `:function` up to about 50 levels deep. | |
19303 | 753 |
22391
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754 [!] is used as with `:function`. Note that |
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755 script-local functions cannot be deleted or redefined |
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756 later in Vim9 script. They can only be removed by |
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757 reloading the same script. |
19181
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758 |
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759 *:enddef* |
21499 | 760 :enddef End of a function defined with `:def`. It should be on |
761 a line by its own. | |
19181
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762 |
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763 |
19473
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764 If the script the function is defined in is Vim9 script, then script-local |
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765 variables can be accessed without the "s:" prefix. They must be defined |
20856 | 766 before the function is compiled. If the script the function is defined in is |
767 legacy script, then script-local variables must be accessed with the "s:" | |
21991 | 768 prefix and they do not need to exist (they can be deleted any time). |
19473
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769 |
20552 | 770 *:defc* *:defcompile* |
771 :defc[ompile] Compile functions defined in the current script that | |
772 were not compiled yet. | |
773 This will report errors found during the compilation. | |
19473
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774 |
19404 | 775 *:disa* *:disassemble* |
776 :disa[ssemble] {func} Show the instructions generated for {func}. | |
777 This is for debugging and testing. | |
19556
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|
778 Note that for command line completion of {func} you |
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779 can prepend "s:" to find script-local functions. |
19404 | 780 |
21250 | 781 Limitations ~ |
782 | |
783 Local variables will not be visible to string evaluation. For example: > | |
23358
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784 def MapList(): list<string> |
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785 var list = ['aa', 'bb', 'cc', 'dd'] |
21250 | 786 return range(1, 2)->map('list[v:val]') |
787 enddef | |
788 | |
789 The map argument is a string expression, which is evaluated without the | |
790 function scope. Instead, use a lambda: > | |
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791 def MapList(): list<string> |
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792 var list = ['aa', 'bb', 'cc', 'dd'] |
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793 return range(1, 2)->map(( _, v) => list[v]) |
21250 | 794 enddef |
795 | |
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796 The same is true for commands that are not compiled, such as `:global`. |
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797 For these the backtick expansion can be used. Example: > |
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798 def Replace() |
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799 var newText = 'blah' |
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800 g/pattern/s/^/`=newText`/ |
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801 enddef |
21250 | 802 |
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803 ============================================================================== |
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804 |
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805 4. Types *vim9-types* |
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806 |
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807 THIS IS STILL UNDER DEVELOPMENT - ANYTHING CAN BREAK - ANYTHING CAN CHANGE |
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808 |
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809 The following builtin types are supported: |
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810 bool |
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811 number |
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812 float |
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813 string |
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814 blob |
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815 list<{type}> |
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816 dict<{type}> |
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817 job |
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818 channel |
19646 | 819 func |
19968 | 820 func: {type} |
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821 func({type}, ...) |
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822 func({type}, ...): {type} |
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823 |
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824 Not supported yet: |
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825 tuple<a: {type}, b: {type}, ...> |
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826 |
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827 These types can be used in declarations, but no value will have this type: |
21499 | 828 {type}|{type} {not implemented yet} |
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829 void |
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830 any |
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831 |
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832 There is no array type, use list<{type}> instead. For a list constant an |
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833 efficient implementation is used that avoids allocating lot of small pieces of |
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834 memory. |
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835 |
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836 A partial and function can be declared in more or less specific ways: |
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837 func any kind of function reference, no type |
19968 | 838 checking for arguments or return value |
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839 func: {type} any number and type of arguments with specific |
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840 return type |
19968 | 841 func({type}) function with argument type, does not return |
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842 a value |
19968 | 843 func({type}): {type} function with argument type and return type |
844 func(?{type}) function with type of optional argument, does | |
845 not return a value | |
846 func(...{type}) function with type of variable number of | |
847 arguments, does not return a value | |
848 func({type}, ?{type}, ...{type}): {type} | |
849 function with: | |
850 - type of mandatory argument | |
851 - type of optional argument | |
852 - type of variable number of arguments | |
853 - return type | |
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854 |
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855 If the return type is "void" the function does not return a value. |
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856 |
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857 The reference can also be a |Partial|, in which case it stores extra arguments |
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858 and/or a dictionary, which are not visible to the caller. Since they are |
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859 called in the same way the declaration is the same. |
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860 |
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861 Custom types can be defined with `:type`: > |
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862 :type MyList list<string> |
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863 Custom types must start with a capital letter, to avoid name clashes with |
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864 builtin types added later, similarly to user functions. |
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865 {not implemented yet} |
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866 |
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867 And classes and interfaces can be used as types: > |
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868 :class MyClass |
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869 :var mine: MyClass |
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870 |
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871 :interface MyInterface |
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872 :var mine: MyInterface |
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873 |
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874 :class MyTemplate<Targ> |
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875 :var mine: MyTemplate<number> |
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876 :var mine: MyTemplate<string> |
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877 |
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878 :class MyInterface<Targ> |
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879 :var mine: MyInterface<number> |
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880 :var mine: MyInterface<string> |
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881 {not implemented yet} |
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882 |
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883 |
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884 Variable types and type casting ~ |
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885 *variable-types* |
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886 Variables declared in Vim9 script or in a `:def` function have a type, either |
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887 specified explicitly or inferred from the initialization. |
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888 |
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889 Global, buffer, window and tab page variables do not have a specific type, the |
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890 value can be changed at any time, possibly changing the type. Therefore, in |
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891 compiled code the "any" type is assumed. |
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892 |
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893 This can be a problem when the "any" type is undesired and the actual type is |
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894 expected to always be the same. For example, when declaring a list: > |
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895 var l: list<number> = [1, g:two] |
23305 | 896 At compile time Vim doesn't know the type of "g:two" and the expression type |
897 becomes list<any>. An instruction is generated to check the list type before | |
898 doing the assignment, which is a bit inefficient. | |
899 *type-casting* | |
900 To avoid this, use a type cast: > | |
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901 var l: list<number> = [1, <number>g:two] |
23305 | 902 The compiled code will then only check that "g:two" is a number and give an |
903 error if it isn't. This is called type casting. | |
21717
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904 |
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905 The syntax of a type cast is: "<" {type} ">". There cannot be white space |
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906 after the "<" or before the ">" (to avoid them being confused with |
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907 smaller-than and bigger-than operators). |
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908 |
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909 The semantics is that, if needed, a runtime type check is performed. The |
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910 value is not actually changed. If you need to change the type, e.g. to change |
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911 it to a string, use the |string()| function. Or use |str2nr()| to convert a |
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912 string to a number. |
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913 |
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914 |
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915 Type inference ~ |
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916 *type-inference* |
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917 In general: Whenever the type is clear it can be omitted. For example, when |
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918 declaring a variable and giving it a value: > |
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919 var name = 0 # infers number type |
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920 var name = 'hello' # infers string type |
19181
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921 |
21715
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922 The type of a list and dictionary comes from the common type of the values. |
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923 If the values all have the same type, that type is used for the list or |
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924 dictionary. If there is a mix of types, the "any" type is used. > |
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925 [1, 2, 3] list<number> |
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926 ['a', 'b', 'c'] list<string> |
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927 [1, 'x', 3] list<any> |
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928 |
21991 | 929 |
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930 Stricter type checking ~ |
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931 *type-checking* |
21991 | 932 In legacy Vim script, where a number was expected, a string would be |
933 automatically converted to a number. This was convenient for an actual number | |
934 such as "123", but leads to unexpected problems (but no error message) if the | |
935 string doesn't start with a number. Quite often this leads to hard-to-find | |
936 bugs. | |
937 | |
938 In Vim9 script this has been made stricter. In most places it works just as | |
22171 | 939 before, if the value used matches the expected type. There will sometimes be |
940 an error, thus breaking backwards compatibility. For example: | |
21991 | 941 - Using a number other than 0 or 1 where a boolean is expected. *E1023* |
942 - Using a string value when setting a number options. | |
943 - Using a number where a string is expected. *E1024* | |
944 | |
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945 ============================================================================== |
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946 |
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947 5. Namespace, Import and Export |
19181
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948 *vim9script* *vim9-export* *vim9-import* |
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949 |
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950 THIS IS STILL UNDER DEVELOPMENT - ANYTHING CAN BREAK - ANYTHING CAN CHANGE |
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951 |
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952 A Vim9 script can be written to be imported. This means that everything in |
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953 the script is local, unless exported. Those exported items, and only those |
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954 items, can then be imported in another script. |
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955 |
21991 | 956 You can cheat by using the global namespace explicitly. We will assume here |
957 that you don't do that. | |
958 | |
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959 |
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960 Namespace ~ |
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961 *:vim9script* *:vim9* |
19303 | 962 To recognize a file that can be imported the `vim9script` statement must |
19181
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963 appear as the first statement in the file. It tells Vim to interpret the |
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964 script in its own namespace, instead of the global namespace. If a file |
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965 starts with: > |
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966 vim9script |
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967 var myvar = 'yes' |
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968 Then "myvar" will only exist in this file. While without `vim9script` it would |
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969 be available as `g:myvar` from any other script and function. |
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970 |
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971 The variables at the file level are very much like the script-local "s:" |
20115 | 972 variables in legacy Vim script, but the "s:" is omitted. And they cannot be |
973 deleted. | |
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974 |
20115 | 975 In Vim9 script the global "g:" namespace can still be used as before. And the |
976 "w:", "b:" and "t:" namespaces. These have in common that variables are not | |
977 declared and they can be deleted. | |
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978 |
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979 A side effect of `:vim9script` is that the 'cpoptions' option is set to the |
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980 Vim default value, like with: > |
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981 :set cpo&vim |
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982 One of the effects is that |line-continuation| is always enabled. |
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983 The original value of 'cpoptions' is restored at the end of the script. |
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984 |
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985 |
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986 Export ~ |
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987 *:export* *:exp* |
21499 | 988 Exporting an item can be written as: > |
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989 export const EXPORTED_CONST = 1234 |
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990 export var someValue = ... |
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991 export final someValue = ... |
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992 export const someValue = ... |
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993 export def MyFunc() ... |
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994 export class MyClass ... |
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995 |
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996 As this suggests, only constants, variables, `:def` functions and classes can |
21499 | 997 be exported. {classes are not implemented yet} |
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998 |
20856 | 999 *E1042* |
1000 `:export` can only be used in Vim9 script, at the script level. | |
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1001 |
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1002 |
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1003 Import ~ |
20965 | 1004 *:import* *:imp* *E1094* |
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1005 The exported items can be imported individually in another Vim9 script: > |
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1006 import EXPORTED_CONST from "thatscript.vim" |
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1007 import MyClass from "myclass.vim" |
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1008 |
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1009 To import multiple items at the same time: > |
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1010 import {someValue, MyClass} from "thatscript.vim" |
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1011 |
19303 | 1012 In case the name is ambiguous, another name can be specified: > |
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1013 import MyClass as ThatClass from "myclass.vim" |
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1014 import {someValue, MyClass as ThatClass} from "myclass.vim" |
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1015 |
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1016 To import all exported items under a specific identifier: > |
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1017 import * as That from 'thatscript.vim' |
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1018 |
22328 | 1019 {not implemented yet: using "This as That"} |
1020 | |
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1021 Then you can use "That.EXPORTED_CONST", "That.someValue", etc. You are free |
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1022 to choose the name "That", but it is highly recommended to use the name of the |
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1023 script file to avoid confusion. |
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1024 |
22171 | 1025 `:import` can also be used in legacy Vim script. The imported items still |
1026 become script-local, even when the "s:" prefix is not given. | |
1027 | |
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1028 The script name after `import` can be: |
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1029 - A relative path, starting "." or "..". This finds a file relative to the |
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1030 location of the script file itself. This is useful to split up a large |
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1031 plugin into several files. |
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1032 - An absolute path, starting with "/" on Unix or "D:/" on MS-Windows. This |
22723 | 1033 will rarely be used. |
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1034 - A path not being relative or absolute. This will be found in the |
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1035 "import" subdirectories of 'runtimepath' entries. The name will usually be |
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1036 longer and unique, to avoid loading the wrong file. |
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1037 |
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1038 Once a vim9 script file has been imported, the result is cached and used the |
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1039 next time the same script is imported. It will not be read again. |
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1040 *:import-cycle* |
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1041 The `import` commands are executed when encountered. If that script (directly |
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1042 or indirectly) imports the current script, then items defined after the |
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1043 `import` won't be processed yet. Therefore cyclic imports can exist, but may |
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1044 result in undefined items. |
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1045 |
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1046 |
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1047 Import in an autoload script ~ |
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1048 |
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1049 For optimal startup speed, loading scripts should be postponed until they are |
19303 | 1050 actually needed. A recommended mechanism: |
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1051 |
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1052 1. In the plugin define user commands, functions and/or mappings that refer to |
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1053 an autoload script. > |
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1054 command -nargs=1 SearchForStuff call searchfor#Stuff(<f-args>) |
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1055 |
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1056 < This goes in .../plugin/anyname.vim. "anyname.vim" can be freely chosen. |
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1057 |
21825 | 1058 2. In the autoload script do the actual work. You can import items from |
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1059 other files to split up functionality in appropriate pieces. > |
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1060 vim9script |
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1061 import FilterFunc from "../import/someother.vim" |
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1062 def searchfor#Stuff(arg: string) |
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1063 var filtered = FilterFunc(arg) |
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1064 ... |
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1065 < This goes in .../autoload/searchfor.vim. "searchfor" in the file name |
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1066 must be exactly the same as the prefix for the function name, that is how |
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1067 Vim finds the file. |
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1068 |
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1069 3. Other functionality, possibly shared between plugins, contains the exported |
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1070 items and any private items. > |
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1071 vim9script |
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1072 var localVar = 'local' |
22171 | 1073 export def FilterFunc(arg: string): string |
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1074 ... |
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1075 < This goes in .../import/someother.vim. |
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1076 |
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1077 When compiling a `:def` function and a function in an autoload script is |
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1078 encountered, the script is not loaded until the `:def` function is called. |
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1079 |
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1080 |
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1081 Import in legacy Vim script ~ |
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1082 |
20856 | 1083 If an `import` statement is used in legacy Vim script, the script-local "s:" |
1084 namespace will be used for the imported item, even when "s:" is not specified. | |
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1085 |
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1086 |
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1087 ============================================================================== |
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1088 |
22328 | 1089 6. Future work: classes *vim9-classes* |
1090 | |
1091 Above "class" was mentioned a few times, but it has not been implemented yet. | |
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1092 Most of Vim9 script can be created without this functionality, and since |
22328 | 1093 implementing classes is going to be a lot of work, it is left for the future. |
1094 For now we'll just make sure classes can be added later. | |
1095 | |
1096 Thoughts: | |
1097 - `class` / `endclass`, everything in one file | |
1098 - Class names are always CamelCase | |
1099 - Single constructor | |
1100 - Single inheritance with `class ThisClass extends BaseClass` | |
1101 - `abstract class` | |
1102 - `interface` (Abstract class without any implementation) | |
1103 - `class SomeClass implements SomeInterface` | |
1104 - Generics for class: `class <Tkey, Tentry>` | |
1105 - Generics for function: `def <Tkey> GetLast(key: Tkey)` | |
1106 | |
1107 Again, much of this is from TypeScript. | |
1108 | |
1109 Some things that look like good additions: | |
1110 - Use a class as an interface (like Dart) | |
1111 - Extend a class with methods, using an import (like Dart) | |
1112 | |
1113 An important class that will be provided is "Promise". Since Vim is single | |
1114 threaded, connecting asynchronous operations is a natural way of allowing | |
1115 plugins to do their work without blocking the user. It's a uniform way to | |
1116 invoke callbacks and handle timeouts and errors. | |
1117 | |
1118 ============================================================================== | |
1119 | |
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1120 9. Rationale *vim9-rationale* |
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1121 |
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1122 The :def command ~ |
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1123 |
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1124 Plugin writers have asked for much faster Vim script. Investigations have |
19303 | 1125 shown that keeping the existing semantics of function calls make this close to |
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1126 impossible, because of the overhead involved with calling a function, setting |
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1127 up the local function scope and executing lines. There are many details that |
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1128 need to be handled, such as error messages and exceptions. The need to create |
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1129 a dictionary for a: and l: scopes, the a:000 list and several others add too |
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1130 much overhead that cannot be avoided. |
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1131 |
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1132 Therefore the `:def` method to define a new-style function had to be added, |
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1133 which allows for a function with different semantics. Most things still work |
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1134 as before, but some parts do not. A new way to define a function was |
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1135 considered the best way to separate the legacy style code from Vim9 style code. |
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1136 |
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1137 Using "def" to define a function comes from Python. Other languages use |
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1138 "function" which clashes with legacy Vim script. |
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1139 |
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1140 |
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1141 Type checking ~ |
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1142 |
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1143 When compiling lines of Vim commands into instructions as much as possible |
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1144 should be done at compile time. Postponing it to runtime makes the execution |
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1145 slower and means mistakes are found only later. For example, when |
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1146 encountering the "+" character and compiling this into a generic add |
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1147 instruction, at execution time the instruction would have to inspect the type |
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1148 of the arguments and decide what kind of addition to do. And when the |
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1149 type is dictionary throw an error. If the types are known to be numbers then |
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1150 an "add number" instruction can be used, which is faster. The error can be |
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1151 given at compile time, no error handling is needed at runtime, since adding |
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1152 two numbers cannot fail. |
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1153 |
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1154 The syntax for types, using <type> for compound types, is similar to Java. It |
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1155 is easy to understand and widely used. The type names are what were used in |
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1156 Vim before, with some additions such as "void" and "bool". |
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1157 |
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1158 |
22328 | 1159 Removing clutter and weirdness ~ |
20856 | 1160 |
22328 | 1161 Once decided that `:def` functions have different syntax than legacy functions, |
1162 we are free to add improvements to make the code more familiar for users who | |
1163 know popular programming languages. In other words: remove weird things that | |
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1164 only Vim does. |
22328 | 1165 |
1166 We can also remove clutter, mainly things that were done to make Vim script | |
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1167 backwards compatible with the good old Vi commands. |
20856 | 1168 |
22328 | 1169 Examples: |
1170 - Drop `:call` for calling a function and `:eval` for manipulating data. | |
1171 - Drop using a leading backslash for line continuation, automatically figure | |
1172 out where an expression ends. | |
20856 | 1173 |
22328 | 1174 However, this does require that some things need to change: |
1175 - Comments start with # instead of ", to avoid confusing them with strings. | |
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1176 This is good anyway, it is known from several popular languages. |
22328 | 1177 - Ex command ranges need to be prefixed with a colon, to avoid confusion with |
1178 expressions (single quote can be a string or a mark, "/" can be divide or a | |
1179 search command, etc.). | |
1180 | |
1181 Goal is to limit the differences. A good criteria is that when the old syntax | |
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1182 is accidentally used you are very likely to get an error message. |
20856 | 1183 |
1184 | |
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1185 Syntax and semantics from popular languages ~ |
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1186 |
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1187 Script writers have complained that the Vim script syntax is unexpectedly |
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1188 different from what they are used to. To reduce this complaint popular |
20856 | 1189 languages are used as an example. At the same time, we do not want to abandon |
1190 the well-known parts of legacy Vim script. | |
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1191 |
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1192 For many things TypeScript is followed. It's a recent language that is |
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1193 gaining popularity and has similarities with Vim script. It also has a |
22328 | 1194 mix of static typing (a variable always has a known value type) and dynamic |
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1195 typing (a variable can have different types, this changes at runtime). Since |
22328 | 1196 legacy Vim script is dynamically typed and a lot of existing functionality |
1197 (esp. builtin functions) depends on that, while static typing allows for much | |
1198 faster execution, we need to have this mix in Vim9 script. | |
1199 | |
22171 | 1200 There is no intention to completely match TypeScript syntax and semantics. We |
1201 just want to take those parts that we can use for Vim and we expect Vim users | |
22328 | 1202 will be happy with. TypeScript is a complex language with its own history, |
1203 advantages and disadvantages. To get an idea of the disadvantages read the | |
1204 book: "JavaScript: The Good Parts". Or find the article "TypeScript: the good | |
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1205 parts" and read the "Things to avoid" section. |
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1206 |
22328 | 1207 People familiar with other languages (Java, Python, etc.) will also find |
1208 things in TypeScript that they do not like or do not understand. We'll try to | |
1209 avoid those things. | |
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1210 |
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1211 Specific items from TypeScript we avoid: |
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1212 - Overloading "+", using it both for addition and string concatenation. This |
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1213 goes against legacy Vim script and often leads to mistakes. For that reason |
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1214 we will keep using ".." for string concatenation. Lua also uses ".." this |
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1215 way. And it allows for conversion to string for more values. |
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1216 - TypeScript can use an expression like "99 || 'yes'" in a condition, but |
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1217 cannot assign the value to a boolean. That is inconsistent and can be |
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1218 annoying. Vim recognizes an expression with && or || and allows using the |
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1219 result as a bool. TODO: to be reconsidered |
22272
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1220 - TypeScript considers an empty string as Falsy, but an empty list or dict as |
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1221 Truthy. That is inconsistent. In Vim an empty list and dict are also |
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1222 Falsy. |
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1223 - TypeScript has various "Readonly" types, which have limited usefulness, |
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1224 since a type cast can remove the immutable nature. Vim locks the value, |
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1225 which is more flexible, but is only checked at runtime. |
22171 | 1226 |
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1227 |
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1228 Declarations ~ |
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1229 |
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1230 Legacy Vim script uses `:let` for every assignment, while in Vim9 declarations |
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1231 are used. That is different, thus it's good to use a different command: |
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1232 `:var`. This is used in many languages. The semantics might be slightly |
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1233 different, but it's easily recognized as a declaration. |
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1234 |
23047 | 1235 Using `:const` for constants is common, but the semantics varies. Some |
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1236 languages only make the variable immutable, others also make the value |
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1237 immutable. Since "final" is well known from Java for only making the variable |
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1238 immutable we decided to use that. And then `:const` can be used for making |
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1239 both immutable. This was also used in legacy Vim script and the meaning is |
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1240 almost the same. |
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1241 |
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1242 What we end up with is very similar to Dart: > |
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1243 :var name # mutable variable and value |
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1244 :final name # immutable variable, mutable value |
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1245 :const name # immutable variable and value |
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1246 |
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1247 Since legacy and Vim9 script will be mixed and global variables will be |
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1248 shared, optional type checking is desirable. Also, type inference will avoid |
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1249 the need for specifying the type in many cases. The TypeScript syntax fits |
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1250 best for adding types to declarations: > |
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1251 var name: string # string type is specified |
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1252 ... |
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1253 name = 'John' |
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1254 const greeting = 'hello' # string type is inferred |
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1255 |
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1256 This is how we put types in a declaration: > |
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1257 var mylist: list<string> |
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1258 final mylist: list<string> = ['foo'] |
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1259 def Func(arg1: number, arg2: string): bool |
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1260 |
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1261 Two alternatives were considered: |
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1262 1. Put the type before the name, like Dart: > |
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1263 var list<string> mylist |
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1264 final list<string> mylist = ['foo'] |
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1265 def Func(number arg1, string arg2) bool |
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1266 2. Put the type after the variable name, but do not use a colon, like Go: > |
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1267 var mylist list<string> |
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1268 final mylist list<string> = ['foo'] |
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1269 def Func(arg1 number, arg2 string) bool |
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1270 |
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1271 The first is more familiar for anyone used to C or Java. The second one |
22565 | 1272 doesn't really have an advantage over the first, so let's discard the second. |
22391
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1273 |
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1274 Since we use type inference the type can be left out when it can be inferred |
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1275 from the value. This means that after `var` we don't know if a type or a name |
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1276 follows. That makes parsing harder, not only for Vim but also for humans. |
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1277 Also, it will not be allowed to use a variable name that could be a type name, |
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1278 using `var string string` is too confusing. |
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1279 |
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1280 The chosen syntax, using a colon to separate the name from the type, adds |
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1281 punctuation, but it actually makes it easier to recognize the parts of a |
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1282 declaration. |
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1283 |
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1284 |
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1285 Expressions ~ |
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1286 |
22565 | 1287 Expression evaluation was already close to what other languages are doing. |
1288 Some details are unexpected and can be improved. For example a boolean | |
1289 condition would accept a string, convert it to a number and check if the | |
1290 number is non-zero. This is unexpected and often leads to mistakes, since | |
1291 text not starting with a number would be converted to zero, which is | |
22723 | 1292 considered false. Thus using a string for a condition would often not give an |
1293 error and be considered false. That is confusing. | |
22391
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1294 |
23047 | 1295 In Vim9 type checking is stricter to avoid mistakes. Where a condition is |
22565 | 1296 used, e.g. with the `:if` command and the `||` operator, only boolean-like |
1297 values are accepted: | |
1298 true: `true`, `v:true`, `1`, `0 < 9` | |
1299 false: `false`, `v:false`, `0`, `0 > 9` | |
1300 Note that the number zero is false and the number one is true. This is more | |
22723 | 1301 permissive than most other languages. It was done because many builtin |
22565 | 1302 functions return these values. |
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1303 |
22565 | 1304 If you have any type of value and want to use it as a boolean, use the `!!` |
1305 operator: | |
1306 true: !`!'text'`, `!![99]`, `!!{'x': 1}`, `!!99` | |
1307 false: `!!''`, `!![]`, `!!{}` | |
1308 | |
1309 From a language like JavaScript we have this handy construct: > | |
1310 GetName() || 'unknown' | |
1311 However, this conflicts with only allowing a boolean for a condition. | |
1312 Therefore the "??" operator was added: > | |
1313 GetName() ?? 'unknown' | |
1314 Here you can explicitly express your intention to use the value as-is and not | |
1315 result in a boolean. This is called the |falsy-operator|. | |
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1316 |
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1317 |
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1318 Import and Export ~ |
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1319 |
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1320 A problem of legacy Vim script is that by default all functions and variables |
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1321 are global. It is possible to make them script-local, but then they are not |
22171 | 1322 available in other scripts. This defies the concept of a package that only |
1323 exports selected items and keeps the rest local. | |
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1324 |
21825 | 1325 In Vim9 script a mechanism very similar to the JavaScript import and export |
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1326 mechanism is supported. It is a variant to the existing `:source` command |
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1327 that works like one would expect: |
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1328 - Instead of making everything global by default, everything is script-local, |
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1329 unless exported. |
22171 | 1330 - When importing a script the symbols that are imported are explicitly listed, |
1331 avoiding name conflicts and failures if functionality is added later. | |
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1332 - The mechanism allows for writing a big, long script with a very clear API: |
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1333 the exported function(s) and class(es). |
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1334 - By using relative paths loading can be much faster for an import inside of a |
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1335 package, no need to search many directories. |
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1336 - Once an import has been used, it can be cached and loading it again can be |
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1337 avoided. |
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1338 - The Vim-specific use of "s:" to make things script-local can be dropped. |
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1339 |
20856 | 1340 When sourcing a Vim9 script from a legacy script, only the items defined |
1341 globally can be used, not the exported items. Alternatives considered: | |
1342 - All the exported items become available as script-local items. This makes | |
22171 | 1343 it uncontrollable what items get defined and likely soon leads to trouble. |
20856 | 1344 - Use the exported items and make them global. Disadvantage is that it's then |
1345 not possible to avoid name clashes in the global namespace. | |
1346 - Completely disallow sourcing a Vim9 script, require using `:import`. That | |
1347 makes it difficult to use scripts for testing, or sourcing them from the | |
1348 command line to try them out. | |
22171 | 1349 Note that you can also use `:import` in legacy Vim script, see above. |
20856 | 1350 |
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1351 |
22328 | 1352 Compiling functions early ~ |
1353 | |
1354 Functions are compiled when called or when `:defcompile` is used. Why not | |
1355 compile them early, so that syntax and type errors are reported early? | |
1356 | |
1357 The functions can't be compiled right away when encountered, because there may | |
1358 be forward references to functions defined later. Consider defining functions | |
1359 A, B and C, where A calls B, B calls C, and C calls A again. It's impossible | |
1360 to reorder the functions to avoid forward references. | |
1361 | |
1362 An alternative would be to first scan through the file to locate items and | |
1363 figure out their type, so that forward references are found, and only then | |
1364 execute the script and compile the functions. This means the script has to be | |
1365 parsed twice, which is slower, and some conditions at the script level, such | |
1366 as checking if a feature is supported, are hard to use. An attempt was made | |
1367 to see if it works, but it turned out to be impossible to make work nicely. | |
1368 | |
1369 It would be possible to compile all the functions at the end of the script. | |
1370 The drawback is that if a function never gets called, the overhead of | |
1371 compiling it counts anyway. Since startup speed is very important, in most | |
1372 cases it's better to do it later and accept that syntax and type errors are | |
1373 only reported then. In case these errors should be found early, e.g. when | |
1374 testing, the `:defcompile` command will help out. | |
1375 | |
1376 | |
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1377 Why not use an embedded language? ~ |
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1378 |
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1379 Vim supports interfaces to Perl, Python, Lua, Tcl and a few others. But |
22328 | 1380 these interfaces have never become widely used, for various reasons. When |
1381 Vim9 was designed a decision was made to make these interfaces lower priority | |
1382 and concentrate on Vim script. | |
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1383 |
22328 | 1384 Still, plugin writers may find other languages more familiar, want to use |
1385 existing libraries or see a performance benefit. We encourage plugin authors | |
1386 to write code in any language and run it as an external tool, using jobs and | |
1387 channels. We can try to make this easier somehow. | |
1388 | |
1389 Using an external tool also has disadvantages. An alternative is to convert | |
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1390 the tool into Vim script. For that to be possible without too much |
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1391 translation, and keeping the code fast at the same time, the constructs of the |
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1392 tool need to be supported. Since most languages support classes the lack of |
22171 | 1393 support for classes in Vim is then a problem. |
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1394 |
22328 | 1395 |
1396 Classes ~ | |
1397 | |
1398 Vim supports a kind-of object oriented programming by adding methods to a | |
1399 dictionary. With some care this can be made to work, but it does not look | |
1400 like real classes. On top of that, it's quite slow, because of the use of | |
1401 dictionaries. | |
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1402 |
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1403 The support of classes in Vim9 script is a "minimal common functionality" of |
22171 | 1404 class support in most languages. It works much like Java, which is the most |
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1405 popular programming language. |
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1406 |
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1407 |
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1408 |
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1409 vim:tw=78:ts=8:noet:ft=help:norl: |