Mercurial > vim
annotate runtime/doc/vim9.txt @ 23305:fab58304f77d
Update runtime files.
Commit: https://github.com/vim/vim/commit/4072ba571babd733d1800c082416fe8fe3c28ed7
Author: Bram Moolenaar <Bram@vim.org>
Date: Wed Dec 23 13:56:35 2020 +0100
Update runtime files.
author | Bram Moolenaar <Bram@vim.org> |
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date | Wed, 23 Dec 2020 14:00:04 +0100 |
parents | 99ef85ff1af4 |
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rev | line source |
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23305 | 1 *vim9.txt* For Vim version 8.2. Last change: 2020 Dec 23 |
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4 VIM REFERENCE MANUAL by Bram Moolenaar |
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5 |
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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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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. |
20115 | 116 |
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117 |
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118 Vim9 functions ~ |
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119 |
20241 | 120 A function defined with `:def` is compiled. Execution is many times faster, |
121 often 10x to 100x times. | |
122 | |
20552 | 123 Many errors are already found when compiling, before the function is executed. |
20241 | 124 The syntax is strict, to enforce code that is easy to read and understand. |
125 | |
23164 | 126 Compilation is done when either of these is encountered: |
127 - the first time the function is called | |
21991 | 128 - when the `:defcompile` command is encountered in the script where the |
129 function was defined | |
130 - `:disassemble` is used for the function. | |
131 - a function that is compiled calls the function or uses it as a function | |
132 reference | |
20552 | 133 |
134 `:def` has no options like `:function` does: "range", "abort", "dict" or | |
23164 | 135 "closure". A `:def` function always aborts on an error (unless `:silent!` was |
136 used for the command or inside a `:try` block), does not get a range passed | |
23305 | 137 cannot be a "dict" function, and can always be a closure. |
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138 |
20241 | 139 The argument types and return type need to be specified. The "any" type can |
140 be used, type checking will then be done at runtime, like with legacy | |
141 functions. | |
142 | |
21825 | 143 Arguments are accessed by name, without "a:", just like any other language. |
144 There is no "a:" dictionary or "a:000" list. | |
20241 | 145 |
146 Variable arguments are defined as the last argument, with a name and have a | |
21825 | 147 list type, similar to TypeScript. For example, a list of numbers: > |
22171 | 148 def MyFunc(...itemlist: list<number>) |
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149 for item in itemlist |
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150 ... |
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151 |
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152 |
20241 | 153 Functions and variables are script-local by default ~ |
20856 | 154 *vim9-scopes* |
20115 | 155 When using `:function` or `:def` to specify a new function at the script level |
156 in a Vim9 script, the function is local to the script, as if "s:" was | |
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157 prefixed. Using the "s:" prefix is optional. To define a global function or |
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158 variable the "g:" prefix must be used. For functions in an autoload script |
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159 the "name#" prefix is sufficient. > |
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160 def ThisFunction() # script-local |
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161 def s:ThisFunction() # script-local |
22171 | 162 def g:ThatFunction() # global |
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163 def scriptname#function() # autoload |
20115 | 164 |
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165 When using `:function` or `:def` to specify a nested function inside a `:def` |
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166 function, this nested function is local to the code block it is defined in. |
22565 | 167 In a `:def` function it is not possible to define a script-local function. It |
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168 is possible to define a global function by using the "g:" prefix. |
20115 | 169 |
170 When referring to a function and no "s:" or "g:" prefix is used, Vim will | |
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171 search for the function: |
22565 | 172 - in the function scope, in block scopes |
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173 - in the script scope, possibly imported |
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174 - in the list of global functions |
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175 However, it is recommended to always use "g:" to refer to a global function |
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176 for clarity. |
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177 |
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178 In all cases the function must be defined before used. That is when it is |
22723 | 179 called, when `:defcompile` causes it to be compiled, or when code that calls |
180 it is being compiled (to figure out the return type). | |
20241 | 181 |
21676 | 182 The result is that functions and variables without a namespace can usually be |
20241 | 183 found in the script, either defined there or imported. Global functions and |
21676 | 184 variables could be defined anywhere (good luck finding out where!). |
20115 | 185 |
21825 | 186 Global functions can still be defined and deleted at nearly any time. In |
20317 | 187 Vim9 script script-local functions are defined once when the script is sourced |
20552 | 188 and cannot be deleted or replaced. |
20115 | 189 |
23305 | 190 When compiling a function and a function call is encountered for a function |
191 that is not (yet) defined, the |FuncUndefined| autocommand is not triggered. | |
192 You can use an autoload function if needed, or call a legacy function and have | |
193 |FuncUndefined| triggered there. | |
194 | |
20115 | 195 |
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196 Variable declarations with :var, :final and :const ~ |
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197 *vim9-declaration* *:var* |
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198 Local variables need to be declared with `:var`. Local constants need to be |
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199 declared with `:final` or `:const`. We refer to both as "variables" in this |
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200 section. |
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201 |
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202 Variables can be local to a script, function or code block: > |
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203 vim9script |
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204 var script_var = 123 |
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205 def SomeFunc() |
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206 var func_var = script_var |
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207 if cond |
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208 var block_var = func_var |
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209 ... |
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210 |
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211 The variables are only visible in the block where they are defined and nested |
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212 blocks. Once the block ends the variable is no longer accessible: > |
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213 if cond |
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214 var inner = 5 |
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215 else |
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216 var inner = 0 |
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217 endif |
22171 | 218 echo inner # Error! |
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219 |
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220 The declaration must be done earlier: > |
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221 var inner: number |
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222 if cond |
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223 inner = 5 |
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224 else |
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225 inner = 0 |
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226 endif |
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227 echo inner |
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228 |
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229 To intentionally hide a variable from code that follows, a block can be |
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230 used: > |
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231 { |
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232 var temp = 'temp' |
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233 ... |
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234 } |
22171 | 235 echo temp # Error! |
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236 |
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237 Declaring a variable with a type but without an initializer will initialize to |
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238 zero, false or empty. |
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239 |
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240 In Vim9 script `:let` cannot be used. An existing variable is assigned to |
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241 without any command. The same for global, window, tab, buffer and Vim |
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242 variables, because they are not really declared. They can also be deleted |
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243 with `:unlet`. |
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244 |
21676 | 245 Variables and functions cannot shadow previously defined or imported variables |
246 and functions. | |
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247 Variables may shadow Ex commands, rename the variable if needed. |
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248 |
20241 | 249 Global variables and user defined functions must be prefixed with "g:", also |
250 at the script level. > | |
19968 | 251 vim9script |
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252 var script_local = 'text' |
21499 | 253 g:global = 'value' |
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254 var Funcref = g:ThatFunction |
19968 | 255 |
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256 Since `&opt = value` is now assigning a value to option "opt", ":&" cannot be |
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257 used to repeat a `:substitute` command. |
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258 |
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259 |
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260 Constants ~ |
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261 *vim9-const* *vim9-final* |
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262 How constants work varies between languages. Some consider a variable that |
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263 can't be assigned another value a constant. JavaScript is an example. Others |
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264 also make the value immutable, thus when a constant uses a list, the list |
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265 cannot be changed. In Vim9 we can use both. |
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266 |
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267 `:const` is used for making both the variable and the value a constant. Use |
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268 this for composite structures that you want to make sure will not be modified. |
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269 Example: > |
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270 const myList = [1, 2] |
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271 myList = [3, 4] # Error! |
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272 myList[0] = 9 # Error! |
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273 muList->add(3) # Error! |
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274 < *:final* |
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275 `:final` is used for making only the variable a constant, the value can be |
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276 changed. This is well known from Java. Example: > |
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277 final myList = [1, 2] |
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278 myList = [3, 4] # Error! |
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279 myList[0] = 9 # OK |
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280 muList->add(3) # OK |
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281 |
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282 It is common to write constants as ALL_CAPS, but you don't have to. |
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283 |
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284 The constant only applies to the value itself, not what it refers to. > |
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285 final females = ["Mary"] |
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286 const NAMES = [["John", "Peter"], females] |
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287 NAMES[0] = ["Jack"] # Error! |
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288 NAMES[0][0] = "Jack" # Error! |
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289 NAMES[1] = ["Emma"] # Error! |
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290 Names[1][0] = "Emma" # OK, now females[0] == "Emma" |
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291 |
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292 < *E1092* |
21499 | 293 Declaring more than one variable at a time, using the unpack notation, is |
294 currently not supported: > | |
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295 var [v1, v2] = GetValues() # Error! |
21499 | 296 That is because the type needs to be inferred from the list item type, which |
297 isn't that easy. | |
298 | |
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299 |
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300 Omitting :call and :eval ~ |
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301 |
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302 Functions can be called without `:call`: > |
22171 | 303 writefile(lines, 'file') |
19303 | 304 Using `:call` is still possible, but this is discouraged. |
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305 |
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306 A method call without `eval` is possible, so long as the start is an |
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307 identifier or can't be an Ex command. Examples: > |
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308 myList->add(123) |
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309 g:myList->add(123) |
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310 [1, 2, 3]->Process() |
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311 {a: 1, b: 2}->Process() |
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312 "foobar"->Process() |
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313 ("foobar")->Process() |
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314 'foobar'->Process() |
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315 ('foobar')->Process() |
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316 |
21825 | 317 In the rare case there is ambiguity between a function name and an Ex command, |
21676 | 318 prepend ":" to make clear you want to use the Ex command. For example, there |
319 is both the `:substitute` command and the `substitute()` function. When the | |
320 line starts with `substitute(` this will use the function. Prepend a colon to | |
321 use the command instead: > | |
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322 :substitute(pattern (replacement ( |
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323 |
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324 Note that while variables need to be defined before they can be used, |
21825 | 325 functions can be called before being defined. This is required to allow |
326 for cyclic dependencies between functions. It is slightly less efficient, | |
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327 since the function has to be looked up by name. And a typo in the function |
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328 name will only be found when the function is called. |
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329 |
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330 |
19968 | 331 Omitting function() ~ |
332 | |
333 A user defined function can be used as a function reference in an expression | |
334 without `function()`. The argument types and return type will then be checked. | |
335 The function must already have been defined. > | |
336 | |
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337 var Funcref = MyFunction |
19968 | 338 |
339 When using `function()` the resulting type is "func", a function with any | |
340 number of arguments and any return type. The function can be defined later. | |
341 | |
342 | |
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343 Automatic line continuation ~ |
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344 |
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345 In many cases it is obvious that an expression continues on the next line. In |
21676 | 346 those cases there is no need to prefix the line with a backslash |
347 |line-continuation|. For example, when a list spans multiple lines: > | |
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348 var mylist = [ |
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349 'one', |
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350 'two', |
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351 ] |
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352 And when a dict spans multiple lines: > |
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353 var mydict = { |
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354 one: 1, |
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355 two: 2, |
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356 } |
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357 Function call: > |
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358 var result = Func( |
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359 arg1, |
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360 arg2 |
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361 ) |
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362 |
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363 For binary operators in expressions not in [], {} or () a line break is |
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364 possible just before or after the operator. For example: > |
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365 var text = lead |
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366 .. middle |
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367 .. end |
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368 var total = start + |
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369 end - |
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370 correction |
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371 var result = positive |
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372 ? PosFunc(arg) |
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373 : NegFunc(arg) |
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374 |
21499 | 375 For a method call using "->" and a member using a dot, a line break is allowed |
376 before it: > | |
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377 var result = GetBuilder() |
20965 | 378 ->BuilderSetWidth(333) |
379 ->BuilderSetHeight(777) | |
380 ->BuilderBuild() | |
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381 var result = MyDict |
21499 | 382 .member |
20965 | 383 |
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384 < *E1050* |
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385 To make it possible for the operator at the start of the line to be |
21250 | 386 recognized, it is required to put a colon before a range. This will add |
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387 "start" and print: > |
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388 var result = start |
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389 + print |
21250 | 390 Like this: > |
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391 var result = start + print |
21250 | 392 |
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393 This will assign "start" and print a line: > |
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394 var result = start |
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395 :+ print |
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396 |
23047 | 397 Note that the colon is not required for the |+cmd| argument: > |
398 edit +6 fname | |
399 | |
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400 It is also possible to split a function header over multiple lines, in between |
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401 arguments: > |
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402 def MyFunc( |
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403 text: string, |
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404 separator = '-' |
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405 ): string |
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406 |
23305 | 407 Since a continuation line cannot be easily recognized the parsing of commands |
408 has been made sticter. E.g., because of the error in the first line, the | |
409 second line is seen as a separate command: > | |
410 popup_create(some invalid expression, { | |
411 exit_cb: Func}) | |
412 Now "exit_cb: Func})" is actually a valid command: save any changes to the | |
413 file "_cb: Func})" and exit. To avoid this kind of mistake in Vim9 script | |
414 there must be white space between most command names and the argument. | |
415 | |
416 | |
21250 | 417 Notes: |
418 - "enddef" cannot be used at the start of a continuation line, it ends the | |
419 current function. | |
420 - No line break is allowed in the LHS of an assignment. Specifically when | |
421 unpacking a list |:let-unpack|. This is OK: > | |
22171 | 422 [var1, var2] = |
21250 | 423 Func() |
424 < This does not work: > | |
22171 | 425 [var1, |
21250 | 426 var2] = |
427 Func() | |
428 - No line break is allowed in between arguments of an `:echo`, `:execute` and | |
429 similar commands. This is OK: > | |
22171 | 430 echo [1, |
21250 | 431 2] [3, |
432 4] | |
433 < This does not work: > | |
22171 | 434 echo [1, 2] |
21250 | 435 [3, 4] |
436 - No line break is allowed in the arguments of a lambda, between the "{" and | |
437 "->". This is OK: > | |
22171 | 438 filter(list, {k, v -> |
21250 | 439 v > 0}) |
440 < This does not work: > | |
22171 | 441 filter(list, {k, |
21250 | 442 v -> v > 0}) |
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443 |
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444 |
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445 No curly braces expansion ~ |
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446 |
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447 |curly-braces-names| cannot be used. |
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448 |
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449 |
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450 Dictionary literals ~ |
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451 |
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452 Traditionally Vim has supported dictionary literals with a {} syntax: > |
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453 let dict = {'key': value} |
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454 |
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455 Later it became clear that using a simple text key is very common, thus |
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456 literal dictionaries were introduced in a backwards compatible way: > |
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457 let dict = #{key: value} |
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458 |
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459 However, this #{} syntax is unlike any existing language. As it turns out |
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460 that using a literal key is much more common than using an expression, and |
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461 considering that JavaScript uses this syntax, using the {} form for dictionary |
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462 literals is considered a much more useful syntax. In Vim9 script the {} form |
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463 uses literal keys: > |
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464 let dict = {key: value} |
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465 |
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466 This works for alphanumeric characters, underscore and dash. If you want to |
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467 use another character, use a single or double quoted string: > |
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468 let dict = {'key with space': value} |
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469 let dict = {"key\twith\ttabs": value} |
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470 let dict = {'': value} # empty key |
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471 |
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472 In case the key needs to be an expression, square brackets can be used, just |
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473 like in JavaScript: > |
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474 let dict = {["key" .. nr]: value} |
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475 |
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476 |
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477 No :xit, :t, :append, :change or :insert ~ |
19303 | 478 |
21584
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479 These commands are too easily confused with local variable names. |
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480 Instead of `:x` or `:xit` you can use `:exit`. |
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481 Instead of `:t` you can use `:copy`. |
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482 |
19303 | 483 |
484 Comparators ~ | |
485 | |
486 The 'ignorecase' option is not used for comparators that use strings. | |
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487 |
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488 |
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489 White space ~ |
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490 |
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491 Vim9 script enforces proper use of white space. This is no longer allowed: > |
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492 var name=234 # Error! |
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493 var name= 234 # Error! |
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494 var name =234 # Error! |
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495 There must be white space before and after the "=": > |
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496 var name = 234 # OK |
21250 | 497 White space must also be put before the # that starts a comment after a |
498 command: > | |
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499 var name = 234# Error! |
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500 var name = 234 # OK |
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501 |
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502 White space is required around most operators. |
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503 |
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504 White space is not allowed: |
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505 - Between a function name and the "(": > |
22171 | 506 call Func (arg) # Error! |
507 call Func | |
508 \ (arg) # Error! | |
509 call Func(arg) # OK | |
510 call Func( | |
511 \ arg) # OK | |
512 call Func( | |
513 \ arg # OK | |
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514 \ ) |
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515 |
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516 |
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517 Conditions and expressions ~ |
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518 |
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519 Conditions and expressions are mostly working like they do in other languages. |
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520 Some values are different from legacy Vim script: |
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521 value legacy Vim script Vim9 script ~ |
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522 0 falsy falsy |
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523 1 truthy truthy |
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524 99 truthy Error! |
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525 "0" falsy Error! |
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526 "99" truthy Error! |
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527 "text" falsy Error! |
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528 |
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529 For the "??" operator and when using "!" then there is no error, every value |
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530 is either falsy or truthy. This is mostly like JavaScript, except that an |
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531 empty list and dict is falsy: |
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532 |
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533 type truthy when ~ |
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534 bool v:true or 1 |
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535 number non-zero |
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536 float non-zero |
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537 string non-empty |
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538 blob non-empty |
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539 list non-empty (different from JavaScript) |
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540 dictionary non-empty (different from JavaScript) |
19968 | 541 func when there is a function name |
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542 special v:true |
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543 job when not NULL |
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544 channel when not NULL |
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545 class when not NULL |
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546 object when not NULL (TODO: when isTrue() returns v:true) |
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547 |
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548 The boolean operators "||" and "&&" expect the values to be boolean, zero or |
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549 one: > |
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550 1 || false == true |
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551 0 || 1 == true |
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552 0 || false == false |
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553 1 && true == true |
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554 0 && 1 == false |
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555 8 || 0 Error! |
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556 'yes' && 0 Error! |
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557 [] || 99 Error! |
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558 |
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559 When using "!" for inverting, there is no error for using any type and the |
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560 result is a boolean. "!!" can be used to turn any value into boolean: > |
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561 !'yes' == false |
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562 !![] == false |
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563 !![1, 2, 3] == true |
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564 |
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565 When using "`.."` for string concatenation arguments of simple types are |
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566 always converted to string: > |
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567 'hello ' .. 123 == 'hello 123' |
21825 | 568 'hello ' .. v:true == 'hello v:true' |
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569 |
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570 Simple types are string, float, special and bool. For other types |string()| |
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571 can be used. |
22171 | 572 *false* *true* |
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573 In Vim9 script one can use "true" for v:true and "false" for v:false. |
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574 |
21825 | 575 Indexing a string with [idx] or [idx, idx] uses character indexes instead of |
576 byte indexes. Example: > | |
577 echo 'bár'[1] | |
578 In legacy script this results in the character 0xc3 (an illegal byte), in Vim9 | |
579 script this results in the string 'á'. | |
580 | |
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581 |
21093 | 582 What to watch out for ~ |
583 *vim9-gotchas* | |
584 Vim9 was designed to be closer to often used programming languages, but at the | |
585 same time tries to support the legacy Vim commands. Some compromises had to | |
586 be made. Here is a summary of what might be unexpected. | |
587 | |
588 Ex command ranges need to be prefixed with a colon. > | |
22171 | 589 -> # legacy Vim: shifts the previous line to the right |
590 ->func() # Vim9: method call in continuation line | |
591 :-> # Vim9: shifts the previous line to the right | |
21093 | 592 |
22171 | 593 %s/a/b # legacy Vim: substitute on all lines |
21093 | 594 x = alongname |
22171 | 595 % another # Vim9: line continuation without a backslash |
596 :%s/a/b # Vim9: substitute on all lines | |
597 'text'->func() # Vim9: method call | |
598 :'t # legacy Vim: jump to mark m | |
21093 | 599 |
21676 | 600 Some Ex commands can be confused with assignments in Vim9 script: > |
601 g:name = value # assignment | |
602 g:pattern:cmd # invalid command - ERROR | |
603 :g:pattern:cmd # :global command | |
604 | |
21093 | 605 Functions defined with `:def` compile the whole function. Legacy functions |
606 can bail out, and the following lines are not parsed: > | |
607 func Maybe() | |
608 if !has('feature') | |
609 return | |
610 endif | |
611 use-feature | |
612 endfunc | |
613 Vim9 functions are compiled as a whole: > | |
614 def Maybe() | |
615 if !has('feature') | |
616 return | |
617 endif | |
22171 | 618 use-feature # May give compilation error |
21093 | 619 enddef |
620 For a workaround, split it in two functions: > | |
621 func Maybe() | |
622 if has('feature') | |
623 call MaybyInner() | |
624 endif | |
625 endfunc | |
626 if has('feature') | |
627 def MaybeInner() | |
628 use-feature | |
629 enddef | |
630 endif | |
22171 | 631 Or put the unsupported code inside an `if` with a constant expression that |
21991 | 632 evaluates to false: > |
633 def Maybe() | |
634 if has('feature') | |
635 use-feature | |
636 endif | |
637 enddef | |
638 Note that for unrecognized commands there is no check for "|" and a following | |
639 command. This will give an error for missing `endif`: > | |
640 def Maybe() | |
641 if has('feature') | use-feature | endif | |
642 enddef | |
21093 | 643 |
23305 | 644 Other differences ~ |
645 | |
646 Patterns are used like 'magic' is set, unless explicitly overruled. | |
647 The 'edcompatible' option value is not used. | |
648 The 'gdefault' option value is not used. | |
649 | |
650 | |
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651 ============================================================================== |
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652 |
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653 3. New style functions *fast-functions* |
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654 |
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655 THIS IS STILL UNDER DEVELOPMENT - ANYTHING CAN BREAK - ANYTHING CAN CHANGE |
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656 |
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657 *:def* |
21825 | 658 :def[!] {name}([arguments])[: {return-type}] |
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659 Define a new function by the name {name}. The body of |
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660 the function follows in the next lines, until the |
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661 matching `:enddef`. |
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662 |
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663 When {return-type} is omitted or is "void" the |
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664 function is not expected to return anything. |
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665 |
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666 {arguments} is a sequence of zero or more argument |
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667 declarations. There are three forms: |
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668 {name}: {type} |
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669 {name} = {value} |
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670 {name}: {type} = {value} |
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671 The first form is a mandatory argument, the caller |
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672 must always provide them. |
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673 The second and third form are optional arguments. |
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674 When the caller omits an argument the {value} is used. |
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675 |
20856 | 676 The function will be compiled into instructions when |
21499 | 677 called, or when `:disassemble` or `:defcompile` is |
678 used. Syntax and type errors will be produced at that | |
679 time. | |
20856 | 680 |
21499 | 681 It is possible to nest `:def` inside another `:def` or |
682 `:function` up to about 50 levels deep. | |
19303 | 683 |
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684 [!] is used as with `:function`. Note that |
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685 script-local functions cannot be deleted or redefined |
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686 later in Vim9 script. They can only be removed by |
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687 reloading the same script. |
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688 |
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689 *:enddef* |
21499 | 690 :enddef End of a function defined with `:def`. It should be on |
691 a line by its own. | |
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692 |
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693 |
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694 If the script the function is defined in is Vim9 script, then script-local |
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695 variables can be accessed without the "s:" prefix. They must be defined |
20856 | 696 before the function is compiled. If the script the function is defined in is |
697 legacy script, then script-local variables must be accessed with the "s:" | |
21991 | 698 prefix and they do not need to exist (they can be deleted any time). |
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699 |
20552 | 700 *:defc* *:defcompile* |
701 :defc[ompile] Compile functions defined in the current script that | |
702 were not compiled yet. | |
703 This will report errors found during the compilation. | |
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704 |
19404 | 705 *:disa* *:disassemble* |
706 :disa[ssemble] {func} Show the instructions generated for {func}. | |
707 This is for debugging and testing. | |
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708 Note that for command line completion of {func} you |
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709 can prepend "s:" to find script-local functions. |
19404 | 710 |
21250 | 711 Limitations ~ |
712 | |
713 Local variables will not be visible to string evaluation. For example: > | |
714 def EvalString(): list<string> | |
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715 var list = ['aa', 'bb', 'cc', 'dd'] |
21250 | 716 return range(1, 2)->map('list[v:val]') |
717 enddef | |
718 | |
719 The map argument is a string expression, which is evaluated without the | |
720 function scope. Instead, use a lambda: > | |
721 def EvalString(): list<string> | |
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722 var list = ['aa', 'bb', 'cc', 'dd'] |
21250 | 723 return range(1, 2)->map({ _, v -> list[v] }) |
724 enddef | |
725 | |
726 | |
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727 ============================================================================== |
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728 |
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729 4. Types *vim9-types* |
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730 |
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731 THIS IS STILL UNDER DEVELOPMENT - ANYTHING CAN BREAK - ANYTHING CAN CHANGE |
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732 |
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733 The following builtin types are supported: |
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734 bool |
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735 number |
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736 float |
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737 string |
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738 blob |
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739 list<{type}> |
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740 dict<{type}> |
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741 job |
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742 channel |
19646 | 743 func |
19968 | 744 func: {type} |
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745 func({type}, ...) |
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746 func({type}, ...): {type} |
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747 |
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748 Not supported yet: |
19904
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749 tuple<a: {type}, b: {type}, ...> |
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750 |
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751 These types can be used in declarations, but no value will have this type: |
21499 | 752 {type}|{type} {not implemented yet} |
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753 void |
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754 any |
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755 |
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756 There is no array type, use list<{type}> instead. For a list constant an |
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757 efficient implementation is used that avoids allocating lot of small pieces of |
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758 memory. |
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759 |
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760 A partial and function can be declared in more or less specific ways: |
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761 func any kind of function reference, no type |
19968 | 762 checking for arguments or return value |
19904
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763 func: {type} any number and type of arguments with specific |
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764 return type |
19968 | 765 func({type}) function with argument type, does not return |
19904
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766 a value |
19968 | 767 func({type}): {type} function with argument type and return type |
768 func(?{type}) function with type of optional argument, does | |
769 not return a value | |
770 func(...{type}) function with type of variable number of | |
771 arguments, does not return a value | |
772 func({type}, ?{type}, ...{type}): {type} | |
773 function with: | |
774 - type of mandatory argument | |
775 - type of optional argument | |
776 - type of variable number of arguments | |
777 - return type | |
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778 |
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779 If the return type is "void" the function does not return a value. |
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780 |
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781 The reference can also be a |Partial|, in which case it stores extra arguments |
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782 and/or a dictionary, which are not visible to the caller. Since they are |
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783 called in the same way the declaration is the same. |
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784 |
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785 Custom types can be defined with `:type`: > |
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786 :type MyList list<string> |
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787 Custom types must start with a capital letter, to avoid name clashes with |
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788 builtin types added later, similarly to user functions. |
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789 {not implemented yet} |
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790 |
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791 And classes and interfaces can be used as types: > |
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792 :class MyClass |
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793 :var mine: MyClass |
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794 |
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795 :interface MyInterface |
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796 :var mine: MyInterface |
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797 |
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798 :class MyTemplate<Targ> |
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799 :var mine: MyTemplate<number> |
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800 :var mine: MyTemplate<string> |
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801 |
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802 :class MyInterface<Targ> |
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803 :var mine: MyInterface<number> |
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804 :var mine: MyInterface<string> |
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805 {not implemented yet} |
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806 |
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807 |
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808 Variable types and type casting ~ |
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809 *variable-types* |
21717
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810 Variables declared in Vim9 script or in a `:def` function have a type, either |
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811 specified explicitly or inferred from the initialization. |
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812 |
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813 Global, buffer, window and tab page variables do not have a specific type, the |
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814 value can be changed at any time, possibly changing the type. Therefore, in |
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815 compiled code the "any" type is assumed. |
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816 |
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817 This can be a problem when the "any" type is undesired and the actual type is |
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818 expected to always be the same. For example, when declaring a list: > |
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819 var l: list<number> = [1, g:two] |
23305 | 820 At compile time Vim doesn't know the type of "g:two" and the expression type |
821 becomes list<any>. An instruction is generated to check the list type before | |
822 doing the assignment, which is a bit inefficient. | |
823 *type-casting* | |
824 To avoid this, use a type cast: > | |
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825 var l: list<number> = [1, <number>g:two] |
23305 | 826 The compiled code will then only check that "g:two" is a number and give an |
827 error if it isn't. This is called type casting. | |
21717
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828 |
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829 The syntax of a type cast is: "<" {type} ">". There cannot be white space |
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830 after the "<" or before the ">" (to avoid them being confused with |
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831 smaller-than and bigger-than operators). |
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832 |
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833 The semantics is that, if needed, a runtime type check is performed. The |
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834 value is not actually changed. If you need to change the type, e.g. to change |
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835 it to a string, use the |string()| function. Or use |str2nr()| to convert a |
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836 string to a number. |
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837 |
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838 |
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839 Type inference ~ |
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840 *type-inference* |
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841 In general: Whenever the type is clear it can be omitted. For example, when |
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842 declaring a variable and giving it a value: > |
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843 var name = 0 # infers number type |
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844 var name = 'hello' # infers string type |
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845 |
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846 The type of a list and dictionary comes from the common type of the values. |
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847 If the values all have the same type, that type is used for the list or |
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848 dictionary. If there is a mix of types, the "any" type is used. > |
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849 [1, 2, 3] list<number> |
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850 ['a', 'b', 'c'] list<string> |
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851 [1, 'x', 3] list<any> |
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852 |
21991 | 853 |
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854 Stricter type checking ~ |
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855 *type-checking* |
21991 | 856 In legacy Vim script, where a number was expected, a string would be |
857 automatically converted to a number. This was convenient for an actual number | |
858 such as "123", but leads to unexpected problems (but no error message) if the | |
859 string doesn't start with a number. Quite often this leads to hard-to-find | |
860 bugs. | |
861 | |
862 In Vim9 script this has been made stricter. In most places it works just as | |
22171 | 863 before, if the value used matches the expected type. There will sometimes be |
864 an error, thus breaking backwards compatibility. For example: | |
21991 | 865 - Using a number other than 0 or 1 where a boolean is expected. *E1023* |
866 - Using a string value when setting a number options. | |
867 - Using a number where a string is expected. *E1024* | |
868 | |
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869 ============================================================================== |
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870 |
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871 5. Namespace, Import and Export |
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872 *vim9script* *vim9-export* *vim9-import* |
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873 |
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874 THIS IS STILL UNDER DEVELOPMENT - ANYTHING CAN BREAK - ANYTHING CAN CHANGE |
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875 |
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876 A Vim9 script can be written to be imported. This means that everything in |
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877 the script is local, unless exported. Those exported items, and only those |
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878 items, can then be imported in another script. |
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879 |
21991 | 880 You can cheat by using the global namespace explicitly. We will assume here |
881 that you don't do that. | |
882 | |
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883 |
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884 Namespace ~ |
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885 *:vim9script* *:vim9* |
19303 | 886 To recognize a file that can be imported the `vim9script` statement must |
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887 appear as the first statement in the file. It tells Vim to interpret the |
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888 script in its own namespace, instead of the global namespace. If a file |
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889 starts with: > |
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890 vim9script |
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891 var myvar = 'yes' |
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892 Then "myvar" will only exist in this file. While without `vim9script` it would |
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893 be available as `g:myvar` from any other script and function. |
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894 |
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895 The variables at the file level are very much like the script-local "s:" |
20115 | 896 variables in legacy Vim script, but the "s:" is omitted. And they cannot be |
897 deleted. | |
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898 |
20115 | 899 In Vim9 script the global "g:" namespace can still be used as before. And the |
900 "w:", "b:" and "t:" namespaces. These have in common that variables are not | |
901 declared and they can be deleted. | |
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902 |
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903 A side effect of `:vim9script` is that the 'cpoptions' option is set to the |
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904 Vim default value, like with: > |
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905 :set cpo&vim |
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906 One of the effects is that |line-continuation| is always enabled. |
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907 The original value of 'cpoptions' is restored at the end of the script. |
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908 |
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909 |
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910 Export ~ |
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911 *:export* *:exp* |
21499 | 912 Exporting an item can be written as: > |
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913 export const EXPORTED_CONST = 1234 |
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914 export var someValue = ... |
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915 export final someValue = ... |
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916 export const someValue = ... |
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917 export def MyFunc() ... |
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918 export class MyClass ... |
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919 |
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920 As this suggests, only constants, variables, `:def` functions and classes can |
21499 | 921 be exported. {classes are not implemented yet} |
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922 |
20856 | 923 *E1042* |
924 `:export` can only be used in Vim9 script, at the script level. | |
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925 |
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926 |
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927 Import ~ |
20965 | 928 *:import* *:imp* *E1094* |
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929 The exported items can be imported individually in another Vim9 script: > |
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930 import EXPORTED_CONST from "thatscript.vim" |
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931 import MyClass from "myclass.vim" |
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932 |
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933 To import multiple items at the same time: > |
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934 import {someValue, MyClass} from "thatscript.vim" |
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935 |
19303 | 936 In case the name is ambiguous, another name can be specified: > |
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937 import MyClass as ThatClass from "myclass.vim" |
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938 import {someValue, MyClass as ThatClass} from "myclass.vim" |
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939 |
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940 To import all exported items under a specific identifier: > |
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941 import * as That from 'thatscript.vim' |
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942 |
22328 | 943 {not implemented yet: using "This as That"} |
944 | |
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945 Then you can use "That.EXPORTED_CONST", "That.someValue", etc. You are free |
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946 to choose the name "That", but it is highly recommended to use the name of the |
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947 script file to avoid confusion. |
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948 |
22171 | 949 `:import` can also be used in legacy Vim script. The imported items still |
950 become script-local, even when the "s:" prefix is not given. | |
951 | |
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952 The script name after `import` can be: |
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953 - A relative path, starting "." or "..". This finds a file relative to the |
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954 location of the script file itself. This is useful to split up a large |
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955 plugin into several files. |
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956 - An absolute path, starting with "/" on Unix or "D:/" on MS-Windows. This |
22723 | 957 will rarely be used. |
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958 - A path not being relative or absolute. This will be found in the |
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959 "import" subdirectories of 'runtimepath' entries. The name will usually be |
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960 longer and unique, to avoid loading the wrong file. |
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961 |
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962 Once a vim9 script file has been imported, the result is cached and used the |
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963 next time the same script is imported. It will not be read again. |
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964 *:import-cycle* |
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965 The `import` commands are executed when encountered. If that script (directly |
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966 or indirectly) imports the current script, then items defined after the |
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967 `import` won't be processed yet. Therefore cyclic imports can exist, but may |
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968 result in undefined items. |
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969 |
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970 |
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971 Import in an autoload script ~ |
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972 |
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973 For optimal startup speed, loading scripts should be postponed until they are |
19303 | 974 actually needed. A recommended mechanism: |
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975 |
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976 1. In the plugin define user commands, functions and/or mappings that refer to |
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977 an autoload script. > |
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978 command -nargs=1 SearchForStuff call searchfor#Stuff(<f-args>) |
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979 |
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980 < This goes in .../plugin/anyname.vim. "anyname.vim" can be freely chosen. |
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981 |
21825 | 982 2. In the autoload script do the actual work. You can import items from |
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983 other files to split up functionality in appropriate pieces. > |
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984 vim9script |
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985 import FilterFunc from "../import/someother.vim" |
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986 def searchfor#Stuff(arg: string) |
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987 var filtered = FilterFunc(arg) |
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988 ... |
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989 < This goes in .../autoload/searchfor.vim. "searchfor" in the file name |
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990 must be exactly the same as the prefix for the function name, that is how |
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991 Vim finds the file. |
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992 |
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993 3. Other functionality, possibly shared between plugins, contains the exported |
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994 items and any private items. > |
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995 vim9script |
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996 var localVar = 'local' |
22171 | 997 export def FilterFunc(arg: string): string |
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998 ... |
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999 < This goes in .../import/someother.vim. |
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1000 |
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1001 When compiling a `:def` function and a function in an autoload script is |
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1002 encountered, the script is not loaded until the `:def` function is called. |
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1003 |
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1004 |
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1005 Import in legacy Vim script ~ |
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1006 |
20856 | 1007 If an `import` statement is used in legacy Vim script, the script-local "s:" |
1008 namespace will be used for the imported item, even when "s:" is not specified. | |
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1009 |
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1010 |
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1011 ============================================================================== |
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1012 |
22328 | 1013 6. Future work: classes *vim9-classes* |
1014 | |
1015 Above "class" was mentioned a few times, but it has not been implemented yet. | |
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1016 Most of Vim9 script can be created without this functionality, and since |
22328 | 1017 implementing classes is going to be a lot of work, it is left for the future. |
1018 For now we'll just make sure classes can be added later. | |
1019 | |
1020 Thoughts: | |
1021 - `class` / `endclass`, everything in one file | |
1022 - Class names are always CamelCase | |
1023 - Single constructor | |
1024 - Single inheritance with `class ThisClass extends BaseClass` | |
1025 - `abstract class` | |
1026 - `interface` (Abstract class without any implementation) | |
1027 - `class SomeClass implements SomeInterface` | |
1028 - Generics for class: `class <Tkey, Tentry>` | |
1029 - Generics for function: `def <Tkey> GetLast(key: Tkey)` | |
1030 | |
1031 Again, much of this is from TypeScript. | |
1032 | |
1033 Some things that look like good additions: | |
1034 - Use a class as an interface (like Dart) | |
1035 - Extend a class with methods, using an import (like Dart) | |
1036 | |
1037 An important class that will be provided is "Promise". Since Vim is single | |
1038 threaded, connecting asynchronous operations is a natural way of allowing | |
1039 plugins to do their work without blocking the user. It's a uniform way to | |
1040 invoke callbacks and handle timeouts and errors. | |
1041 | |
1042 ============================================================================== | |
1043 | |
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1044 9. Rationale *vim9-rationale* |
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1045 |
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1046 The :def command ~ |
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1047 |
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1048 Plugin writers have asked for much faster Vim script. Investigations have |
19303 | 1049 shown that keeping the existing semantics of function calls make this close to |
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1050 impossible, because of the overhead involved with calling a function, setting |
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1051 up the local function scope and executing lines. There are many details that |
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1052 need to be handled, such as error messages and exceptions. The need to create |
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1053 a dictionary for a: and l: scopes, the a:000 list and several others add too |
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1054 much overhead that cannot be avoided. |
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1055 |
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1056 Therefore the `:def` method to define a new-style function had to be added, |
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1057 which allows for a function with different semantics. Most things still work |
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1058 as before, but some parts do not. A new way to define a function was |
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1059 considered the best way to separate the legacy style code from Vim9 style code. |
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1060 |
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1061 Using "def" to define a function comes from Python. Other languages use |
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1062 "function" which clashes with legacy Vim script. |
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1063 |
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1064 |
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1065 Type checking ~ |
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1066 |
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1067 When compiling lines of Vim commands into instructions as much as possible |
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1068 should be done at compile time. Postponing it to runtime makes the execution |
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1069 slower and means mistakes are found only later. For example, when |
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1070 encountering the "+" character and compiling this into a generic add |
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1071 instruction, at execution time the instruction would have to inspect the type |
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1072 of the arguments and decide what kind of addition to do. And when the |
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1073 type is dictionary throw an error. If the types are known to be numbers then |
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1074 an "add number" instruction can be used, which is faster. The error can be |
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1075 given at compile time, no error handling is needed at runtime, since adding |
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1076 two numbers cannot fail. |
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1077 |
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1078 The syntax for types, using <type> for compound types, is similar to Java. It |
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1079 is easy to understand and widely used. The type names are what were used in |
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1080 Vim before, with some additions such as "void" and "bool". |
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1081 |
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1082 |
22328 | 1083 Removing clutter and weirdness ~ |
20856 | 1084 |
22328 | 1085 Once decided that `:def` functions have different syntax than legacy functions, |
1086 we are free to add improvements to make the code more familiar for users who | |
1087 know popular programming languages. In other words: remove weird things that | |
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1088 only Vim does. |
22328 | 1089 |
1090 We can also remove clutter, mainly things that were done to make Vim script | |
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1091 backwards compatible with the good old Vi commands. |
20856 | 1092 |
22328 | 1093 Examples: |
1094 - Drop `:call` for calling a function and `:eval` for manipulating data. | |
1095 - Drop using a leading backslash for line continuation, automatically figure | |
1096 out where an expression ends. | |
20856 | 1097 |
22328 | 1098 However, this does require that some things need to change: |
1099 - Comments start with # instead of ", to avoid confusing them with strings. | |
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1100 This is good anyway, it is known from several popular languages. |
22328 | 1101 - Ex command ranges need to be prefixed with a colon, to avoid confusion with |
1102 expressions (single quote can be a string or a mark, "/" can be divide or a | |
1103 search command, etc.). | |
1104 | |
1105 Goal is to limit the differences. A good criteria is that when the old syntax | |
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1106 is accidentally used you are very likely to get an error message. |
20856 | 1107 |
1108 | |
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1109 Syntax and semantics from popular languages ~ |
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1110 |
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1111 Script writers have complained that the Vim script syntax is unexpectedly |
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1112 different from what they are used to. To reduce this complaint popular |
20856 | 1113 languages are used as an example. At the same time, we do not want to abandon |
1114 the well-known parts of legacy Vim script. | |
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1115 |
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1116 For many things TypeScript is followed. It's a recent language that is |
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1117 gaining popularity and has similarities with Vim script. It also has a |
22328 | 1118 mix of static typing (a variable always has a known value type) and dynamic |
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1119 typing (a variable can have different types, this changes at runtime). Since |
22328 | 1120 legacy Vim script is dynamically typed and a lot of existing functionality |
1121 (esp. builtin functions) depends on that, while static typing allows for much | |
1122 faster execution, we need to have this mix in Vim9 script. | |
1123 | |
22171 | 1124 There is no intention to completely match TypeScript syntax and semantics. We |
1125 just want to take those parts that we can use for Vim and we expect Vim users | |
22328 | 1126 will be happy with. TypeScript is a complex language with its own history, |
1127 advantages and disadvantages. To get an idea of the disadvantages read the | |
1128 book: "JavaScript: The Good Parts". Or find the article "TypeScript: the good | |
22272
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1129 parts" and read the "Things to avoid" section. |
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1130 |
22328 | 1131 People familiar with other languages (Java, Python, etc.) will also find |
1132 things in TypeScript that they do not like or do not understand. We'll try to | |
1133 avoid those things. | |
22272
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1134 |
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1135 Specific items from TypeScript we avoid: |
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1136 - Overloading "+", using it both for addition and string concatenation. This |
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1137 goes against legacy Vim script and often leads to mistakes. For that reason |
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1138 we will keep using ".." for string concatenation. Lua also uses ".." this |
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1139 way. And it allows for conversion to string for more values. |
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1140 - TypeScript can use an expression like "99 || 'yes'" in a condition, but |
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1141 cannot assign the value to a boolean. That is inconsistent and can be |
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1142 annoying. Vim recognizes an expression with && or || and allows using the |
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1143 result as a bool. TODO: to be reconsidered |
22272
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1144 - TypeScript considers an empty string as Falsy, but an empty list or dict as |
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1145 Truthy. That is inconsistent. In Vim an empty list and dict are also |
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1146 Falsy. |
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1147 - TypeScript has various "Readonly" types, which have limited usefulness, |
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1148 since a type cast can remove the immutable nature. Vim locks the value, |
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1149 which is more flexible, but is only checked at runtime. |
22171 | 1150 |
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1151 |
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1152 Declarations ~ |
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1153 |
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1154 Legacy Vim script uses `:let` for every assignment, while in Vim9 declarations |
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1155 are used. That is different, thus it's good to use a different command: |
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1156 `:var`. This is used in many languages. The semantics might be slightly |
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1157 different, but it's easily recognized as a declaration. |
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1158 |
23047 | 1159 Using `:const` for constants is common, but the semantics varies. Some |
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1160 languages only make the variable immutable, others also make the value |
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1161 immutable. Since "final" is well known from Java for only making the variable |
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1162 immutable we decided to use that. And then `:const` can be used for making |
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1163 both immutable. This was also used in legacy Vim script and the meaning is |
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1164 almost the same. |
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1165 |
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1166 What we end up with is very similar to Dart: > |
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1167 :var name # mutable variable and value |
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1168 :final name # immutable variable, mutable value |
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1169 :const name # immutable variable and value |
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1170 |
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1171 Since legacy and Vim9 script will be mixed and global variables will be |
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1172 shared, optional type checking is desirable. Also, type inference will avoid |
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1173 the need for specifying the type in many cases. The TypeScript syntax fits |
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1174 best for adding types to declarations: > |
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1175 var name: string # string type is specified |
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1176 ... |
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1177 name = 'John' |
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1178 const greeting = 'hello' # string type is inferred |
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1179 |
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1180 This is how we put types in a declaration: > |
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1181 var mylist: list<string> |
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1182 final mylist: list<string> = ['foo'] |
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1183 def Func(arg1: number, arg2: string): bool |
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1184 |
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1185 Two alternatives were considered: |
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1186 1. Put the type before the name, like Dart: > |
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1187 var list<string> mylist |
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1188 final list<string> mylist = ['foo'] |
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1189 def Func(number arg1, string arg2) bool |
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1190 2. Put the type after the variable name, but do not use a colon, like Go: > |
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1191 var mylist list<string> |
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1192 final mylist list<string> = ['foo'] |
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1193 def Func(arg1 number, arg2 string) bool |
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1194 |
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1195 The first is more familiar for anyone used to C or Java. The second one |
22565 | 1196 doesn't really have an advantage over the first, so let's discard the second. |
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1197 |
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1198 Since we use type inference the type can be left out when it can be inferred |
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1199 from the value. This means that after `var` we don't know if a type or a name |
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1200 follows. That makes parsing harder, not only for Vim but also for humans. |
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1201 Also, it will not be allowed to use a variable name that could be a type name, |
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1202 using `var string string` is too confusing. |
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1203 |
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1204 The chosen syntax, using a colon to separate the name from the type, adds |
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1205 punctuation, but it actually makes it easier to recognize the parts of a |
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1206 declaration. |
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1207 |
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1208 |
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1209 Expressions ~ |
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1210 |
22565 | 1211 Expression evaluation was already close to what other languages are doing. |
1212 Some details are unexpected and can be improved. For example a boolean | |
1213 condition would accept a string, convert it to a number and check if the | |
1214 number is non-zero. This is unexpected and often leads to mistakes, since | |
1215 text not starting with a number would be converted to zero, which is | |
22723 | 1216 considered false. Thus using a string for a condition would often not give an |
1217 error and be considered false. That is confusing. | |
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1218 |
23047 | 1219 In Vim9 type checking is stricter to avoid mistakes. Where a condition is |
22565 | 1220 used, e.g. with the `:if` command and the `||` operator, only boolean-like |
1221 values are accepted: | |
1222 true: `true`, `v:true`, `1`, `0 < 9` | |
1223 false: `false`, `v:false`, `0`, `0 > 9` | |
1224 Note that the number zero is false and the number one is true. This is more | |
22723 | 1225 permissive than most other languages. It was done because many builtin |
22565 | 1226 functions return these values. |
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1227 |
22565 | 1228 If you have any type of value and want to use it as a boolean, use the `!!` |
1229 operator: | |
1230 true: !`!'text'`, `!![99]`, `!!{'x': 1}`, `!!99` | |
1231 false: `!!''`, `!![]`, `!!{}` | |
1232 | |
1233 From a language like JavaScript we have this handy construct: > | |
1234 GetName() || 'unknown' | |
1235 However, this conflicts with only allowing a boolean for a condition. | |
1236 Therefore the "??" operator was added: > | |
1237 GetName() ?? 'unknown' | |
1238 Here you can explicitly express your intention to use the value as-is and not | |
1239 result in a boolean. This is called the |falsy-operator|. | |
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1240 |
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1241 |
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1242 Import and Export ~ |
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1243 |
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1244 A problem of legacy Vim script is that by default all functions and variables |
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1245 are global. It is possible to make them script-local, but then they are not |
22171 | 1246 available in other scripts. This defies the concept of a package that only |
1247 exports selected items and keeps the rest local. | |
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1248 |
21825 | 1249 In Vim9 script a mechanism very similar to the JavaScript import and export |
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1250 mechanism is supported. It is a variant to the existing `:source` command |
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1251 that works like one would expect: |
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1252 - Instead of making everything global by default, everything is script-local, |
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1253 unless exported. |
22171 | 1254 - When importing a script the symbols that are imported are explicitly listed, |
1255 avoiding name conflicts and failures if functionality is added later. | |
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1256 - The mechanism allows for writing a big, long script with a very clear API: |
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1257 the exported function(s) and class(es). |
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1258 - By using relative paths loading can be much faster for an import inside of a |
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1259 package, no need to search many directories. |
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1260 - Once an import has been used, it can be cached and loading it again can be |
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1261 avoided. |
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1262 - The Vim-specific use of "s:" to make things script-local can be dropped. |
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1263 |
20856 | 1264 When sourcing a Vim9 script from a legacy script, only the items defined |
1265 globally can be used, not the exported items. Alternatives considered: | |
1266 - All the exported items become available as script-local items. This makes | |
22171 | 1267 it uncontrollable what items get defined and likely soon leads to trouble. |
20856 | 1268 - Use the exported items and make them global. Disadvantage is that it's then |
1269 not possible to avoid name clashes in the global namespace. | |
1270 - Completely disallow sourcing a Vim9 script, require using `:import`. That | |
1271 makes it difficult to use scripts for testing, or sourcing them from the | |
1272 command line to try them out. | |
22171 | 1273 Note that you can also use `:import` in legacy Vim script, see above. |
20856 | 1274 |
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1275 |
22328 | 1276 Compiling functions early ~ |
1277 | |
1278 Functions are compiled when called or when `:defcompile` is used. Why not | |
1279 compile them early, so that syntax and type errors are reported early? | |
1280 | |
1281 The functions can't be compiled right away when encountered, because there may | |
1282 be forward references to functions defined later. Consider defining functions | |
1283 A, B and C, where A calls B, B calls C, and C calls A again. It's impossible | |
1284 to reorder the functions to avoid forward references. | |
1285 | |
1286 An alternative would be to first scan through the file to locate items and | |
1287 figure out their type, so that forward references are found, and only then | |
1288 execute the script and compile the functions. This means the script has to be | |
1289 parsed twice, which is slower, and some conditions at the script level, such | |
1290 as checking if a feature is supported, are hard to use. An attempt was made | |
1291 to see if it works, but it turned out to be impossible to make work nicely. | |
1292 | |
1293 It would be possible to compile all the functions at the end of the script. | |
1294 The drawback is that if a function never gets called, the overhead of | |
1295 compiling it counts anyway. Since startup speed is very important, in most | |
1296 cases it's better to do it later and accept that syntax and type errors are | |
1297 only reported then. In case these errors should be found early, e.g. when | |
1298 testing, the `:defcompile` command will help out. | |
1299 | |
1300 | |
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1301 Why not use an embedded language? ~ |
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1302 |
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1303 Vim supports interfaces to Perl, Python, Lua, Tcl and a few others. But |
22328 | 1304 these interfaces have never become widely used, for various reasons. When |
1305 Vim9 was designed a decision was made to make these interfaces lower priority | |
1306 and concentrate on Vim script. | |
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1307 |
22328 | 1308 Still, plugin writers may find other languages more familiar, want to use |
1309 existing libraries or see a performance benefit. We encourage plugin authors | |
1310 to write code in any language and run it as an external tool, using jobs and | |
1311 channels. We can try to make this easier somehow. | |
1312 | |
1313 Using an external tool also has disadvantages. An alternative is to convert | |
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1314 the tool into Vim script. For that to be possible without too much |
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1315 translation, and keeping the code fast at the same time, the constructs of the |
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1316 tool need to be supported. Since most languages support classes the lack of |
22171 | 1317 support for classes in Vim is then a problem. |
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1318 |
22328 | 1319 |
1320 Classes ~ | |
1321 | |
1322 Vim supports a kind-of object oriented programming by adding methods to a | |
1323 dictionary. With some care this can be made to work, but it does not look | |
1324 like real classes. On top of that, it's quite slow, because of the use of | |
1325 dictionaries. | |
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1326 |
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1327 The support of classes in Vim9 script is a "minimal common functionality" of |
22171 | 1328 class support in most languages. It works much like Java, which is the most |
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1329 popular programming language. |
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1330 |
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1331 |
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1332 |
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1333 vim:tw=78:ts=8:noet:ft=help:norl: |