Mercurial > vim
annotate runtime/doc/vim9class.txt @ 34025:385c61388fc3
runtime(doc): add help tag multiple-constructors. (#13772)
Commit: https://github.com/vim/vim/commit/92feeaffc291d3247fd7c591c5ee4ec1b6c957ec
Author: errael <errael@raelity.com>
Date: Wed Dec 27 10:07:09 2023 -0800
runtime(doc): add help tag multiple-constructors. (https://github.com/vim/vim/issues/13772)
Signed-off-by: Ernie Rael <errael@raelity.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
author | Christian Brabandt <cb@256bit.org> |
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date | Wed, 27 Dec 2023 19:15:06 +0100 |
parents | 291b4ea552eb |
children | cf39f47f26df |
rev | line source |
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1 *vim9class.txt* For Vim version 9.0. Last change: 2023 Dec 25 |
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2 |
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3 |
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4 VIM REFERENCE MANUAL by Bram Moolenaar |
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5 |
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6 |
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7 Vim9 classes, objects, interfaces, types and enums. *vim9-class* |
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8 |
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9 1. Overview |Vim9-class-overview| |
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10 2. A simple class |Vim9-simple-class| |
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11 3. Class variables and methods |Vim9-class-member| |
31885 | 12 4. Using an abstract class |Vim9-abstract-class| |
13 5. Using an interface |Vim9-using-interface| | |
14 6. More class details |Vim9-class| | |
15 7. Type definition |Vim9-type| | |
16 8. Enum |Vim9-enum| | |
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17 |
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18 9. Rationale |
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19 10. To be done later |
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20 |
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21 ============================================================================== |
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22 |
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23 1. Overview *Vim9-class-overview* |
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24 |
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25 The fancy term is "object-oriented programming". You can find lots of study |
31885 | 26 material on this subject. Here we document what |Vim9| script provides, |
27 assuming you know the basics already. Added are helpful hints about how to | |
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28 use this functionality effectively. Vim9 classes and objects cannot be used |
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29 in legacy Vim scripts and legacy functions. |
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30 |
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31 The basic item is an object: |
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32 - An object stores state. It contains one or more variables that can each |
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33 have a value. |
31885 | 34 - An object provides functions that use and manipulate its state. These |
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35 functions are invoked "on the object", which is what sets it apart from the |
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36 traditional separation of data and code that manipulates the data. |
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37 - An object has a well defined interface, with typed member variables and |
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38 methods. |
31885 | 39 - Objects are created from a class and all objects have the same interface. |
40 This does not change at runtime, it is not dynamic. | |
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41 |
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42 An object can only be created by a class. A class provides: |
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43 - A new() method, the constructor, which returns an object for the class. |
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44 This method is invoked on the class name: MyClass.new(). |
31885 | 45 - State shared by all objects of the class: class variables (class members). |
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46 - A hierarchy of classes, with super-classes and sub-classes, inheritance. |
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47 |
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48 An interface is used to specify properties of an object: |
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49 - An object can declare several interfaces that it implements. |
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50 - Different objects implementing the same interface can be used the same way. |
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51 |
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52 The class hierarchy allows for single inheritance. Otherwise interfaces are |
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53 to be used where needed. |
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54 |
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55 |
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56 Class modeling ~ |
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57 |
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58 You can model classes any way you like. Keep in mind what you are building, |
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59 don't try to model the real world. This can be confusing, especially because |
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60 teachers use real-world objects to explain class relations and you might think |
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61 your model should therefore reflect the real world. It doesn't! The model |
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62 should match your purpose. |
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63 |
31885 | 64 Keep in mind that composition (an object contains other objects) is often |
65 better than inheritance (an object extends another object). Don't waste time | |
66 trying to find the optimal class model. Or waste time discussing whether a | |
67 square is a rectangle or that a rectangle is a square. It doesn't matter. | |
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68 |
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69 |
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70 ============================================================================== |
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71 |
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72 2. A simple class *Vim9-simple-class* |
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73 |
31885 | 74 Let's start with a simple example: a class that stores a text position (see |
75 below for how to do this more efficiently): > | |
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76 |
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77 class TextPosition |
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78 var lnum: number |
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79 var col: number |
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80 |
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81 def new(lnum: number, col: number) |
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82 this.lnum = lnum |
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83 this.col = col |
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84 enddef |
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85 |
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86 def SetLnum(lnum: number) |
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87 this.lnum = lnum |
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88 enddef |
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89 |
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90 def SetCol(col: number) |
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91 this.col = col |
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92 enddef |
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93 |
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94 def SetPosition(lnum: number, col: number) |
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95 this.lnum = lnum |
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96 this.col = col |
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97 enddef |
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98 endclass |
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100 You can create an object from this class with the new() method: > |
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101 |
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102 var pos = TextPosition.new(1, 1) |
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103 < |
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104 The object variables "lnum" and "col" can be accessed directly: > |
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105 |
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106 echo $'The text position is ({pos.lnum}, {pos.col})' |
31430 | 107 < *E1317* *E1327* |
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108 If you have been using other object-oriented languages you will notice that in |
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109 Vim, within a class definition, the object members are consistently referred |
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110 to with the "this." prefix. This is different from languages like Java and |
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111 TypeScript. The naming convention makes the object members easy to spot. |
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112 Also, when a variable does not have the "this." prefix you know it is not an |
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113 object variable. |
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114 *E1411* |
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115 From outside the class definition, access an object's methods and variables by |
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116 using the object name followed by a dot following by the member: > |
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117 |
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118 pos.lnum |
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119 pos.setCol(10) |
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120 < |
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121 *E1405* *E1406* |
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122 A class name cannot be used as an expression. A class name cannot be used in |
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123 the left-hand-side of an assignment. |
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125 |
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126 Object variable write access ~ |
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127 *read-only-variable* |
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128 Now try to change an object variable directly: > |
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129 |
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130 pos.lnum = 9 |
31885 | 131 < *E1335* |
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132 This will give you an error! That is because by default object variables can |
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133 be read but not set. That's why the TextPosition class provides a method for |
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134 it: > |
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135 |
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136 pos.SetLnum(9) |
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137 |
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138 Allowing to read but not set an object variable is the most common and safest |
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139 way. Most often there is no problem using a value, while setting a value may |
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140 have side effects that need to be taken care of. In this case, the SetLnum() |
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141 method could check if the line number is valid and either give an error or use |
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142 the closest valid value. |
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143 *:public* *public-variable* *E1331* |
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144 If you don't care about side effects and want to allow the object variable to |
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145 be changed at any time, you can make it public: > |
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146 |
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147 public this.lnum: number |
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149 |
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150 Now you don't need the SetLnum(), SetCol() and SetPosition() methods, setting |
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151 "pos.lnum" directly above will no longer give an error. |
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152 *E1326* |
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153 If you try to set an object variable that doesn't exist you get an error: > |
31579 | 154 pos.other = 9 |
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155 < E1326: Member not found on object "TextPosition": other ~ |
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156 |
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157 *E1376* |
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158 A object variable cannot be accessed using the class name. |
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159 |
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160 Protected variables ~ |
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161 *protected-variable* *E1332* *E1333* |
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162 On the other hand, if you do not want the object variables to be read directly |
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163 from outside the class or its sub-classes, you can make them protected. This |
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164 is done by prefixing an underscore to the name: > |
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165 |
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166 var _lnum: number |
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167 var _col number |
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168 |
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169 Now you need to provide methods to get the value of the protected variables. |
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171 "Get": > |
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172 |
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173 def GetLnum(): number |
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174 return this._lnum |
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175 enddef |
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176 |
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177 def GetCol() number |
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178 return this._col |
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179 enddef |
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180 |
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181 This example isn't very useful, the variables might as well have been public. |
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182 It does become useful if you check the value. For example, restrict the line |
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183 number to the total number of lines: > |
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184 |
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185 def GetLnum(): number |
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186 if this._lnum > this._lineCount |
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187 return this._lineCount |
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188 endif |
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189 return this._lnum |
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190 enddef |
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191 < |
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192 Protected methods ~ |
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193 *protected-method* *E1366* |
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194 If you want object methods to be accessible only from other methods of the |
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195 same class and not used from outside the class, then you can make them |
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196 protected. This is done by prefixing the method name with an underscore: > |
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197 |
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198 class SomeClass |
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199 def _Foo(): number |
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200 return 10 |
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201 enddef |
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202 def Bar(): number |
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203 return this._Foo() |
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204 enddef |
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205 endclass |
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206 < |
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207 Accessing a protected method outside the class will result in an error (using |
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208 the above class): > |
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209 |
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210 var a = SomeClass.new() |
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211 a._Foo() |
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212 < |
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213 Simplifying the new() method ~ |
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214 *new()* *constructor* |
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215 See also |default-constructor| and |multiple-constructors|. |
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216 |
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217 Many constructors take values for the object variables. Thus you very often |
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218 see this pattern: > |
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219 |
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221 var lnum: number |
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222 var col: number |
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223 |
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224 def new(lnum: number, col: number) |
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225 this.lnum = lnum |
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226 this.col = col |
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227 enddef |
31885 | 228 endclass |
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229 < |
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230 *E1390* |
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231 Not only is this text you need to write, it also has the type of each |
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232 variable twice. Since this is so common a shorter way to write new() is |
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233 provided: > |
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234 |
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235 def new(this.lnum, this.col) |
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236 enddef |
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237 |
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238 The semantics are easy to understand: Providing the object variable name, |
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239 including "this.", as the argument to new() means the value provided in the |
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240 new() call is assigned to that object variable. This mechanism comes from the |
31885 | 241 Dart language. |
242 | |
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243 Putting together this way of using new() and making the variables public |
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244 results in a much shorter class definition than what we started with: > |
31885 | 245 |
246 class TextPosition | |
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247 public var lnum: number |
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248 public var col: number |
31885 | 249 |
250 def new(this.lnum, this.col) | |
251 enddef | |
252 | |
253 def SetPosition(lnum: number, col: number) | |
254 this.lnum = lnum | |
255 this.col = col | |
256 enddef | |
257 endclass | |
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258 |
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259 The sequence of constructing a new object is: |
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260 1. Memory is allocated and cleared. All values are zero/false/empty. |
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261 2. For each declared object variable that has an initializer, the expression |
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262 is evaluated and assigned to the variable. This happens in the sequence |
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263 the variables are declared in the class. |
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264 3. Arguments in the new() method in the "this.name" form are assigned. |
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265 4. The body of the new() method is executed. |
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266 |
31885 | 267 If the class extends a parent class, the same thing happens. In the second |
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268 step the object variables of the parent class are initialized first. There is |
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269 no need to call "super()" or "new()" on the parent. |
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270 |
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271 *E1365* |
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272 When defining the new() method the return type should not be specified. It |
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273 always returns an object of the class. |
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274 |
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275 *E1386* |
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276 When invoking an object method, the method name should be preceded by the |
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277 object variable name. An object method cannot be invoked using the class |
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278 name. |
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279 |
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280 ============================================================================== |
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281 |
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282 3. Class Variables and Methods *Vim9-class-member* |
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284 *:static* *E1337* *E1338* *E1368* |
31885 | 285 Class members are declared with "static". They are used by the name without a |
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286 prefix in the class where they are defined: > |
31885 | 287 |
288 class OtherThing | |
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289 var size: number |
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290 static var totalSize: number |
31885 | 291 |
292 def new(this.size) | |
293 totalSize += this.size | |
294 enddef | |
295 endclass | |
296 < *E1340* *E1341* | |
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297 Since the name is used as-is, shadowing the name by a method argument name |
31885 | 298 or local variable name is not allowed. |
299 | |
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300 *E1374* *E1375* *E1384* *E1385* |
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301 To access a class member outside of the class where it is defined, the class |
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302 name prefix must be used. A class member cannot be accessed using an object. |
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303 |
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304 Just like object members the access can be made protected by using an |
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305 underscore as the first character in the name, and it can be made public by |
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306 prefixing "public": > |
31885 | 307 |
308 class OtherThing | |
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309 static var total: number # anybody can read, only class can write |
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310 static var _sum: number # only class can read and write |
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311 public static var result: number # anybody can read and write |
31885 | 312 endclass |
313 < | |
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314 *class-method* |
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315 Class methods are also declared with "static". They can use the class |
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316 variables but they have no access to the object variables, they cannot use the |
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317 "this" keyword: |
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318 > |
31885 | 319 class OtherThing |
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320 var size: number |
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321 static var totalSize: number |
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323 # Clear the total size and return the value it had before. | |
324 static def ClearTotalSize(): number | |
325 var prev = totalSize | |
326 totalSize = 0 | |
327 return prev | |
328 enddef | |
329 endclass | |
330 | |
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331 Inside the class the class method can be called by name directly, outside the |
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332 class the class name must be prefixed: `OtherThing.ClearTotalSize()`. To use |
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333 a super class method in a child class, the class name must be prefixed. |
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335 Just like object methods the access can be made protected by using an |
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336 underscore as the first character in the method name: > |
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337 |
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338 class OtherThing |
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339 static def _Foo() |
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340 echo "Foo" |
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341 enddef |
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342 def Bar() |
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343 _Foo() |
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344 enddef |
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345 endclass |
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346 < |
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347 *E1370* |
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348 Note that constructors cannot be declared as "static". They are called like a |
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349 static but execute as an object method; they have access to "this". |
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350 |
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351 To access the class methods and class variables of a super class in an |
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352 extended class, the class name prefix should be used just as from anywhere |
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353 outside of the defining class: > |
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354 |
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355 vim9script |
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356 class Vehicle |
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357 static var nextID: number = 1000 |
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358 static def GetID(): number |
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359 nextID += 1 |
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360 return nextID |
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361 enddef |
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362 endclass |
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363 class Car extends Vehicle |
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364 var myID: number |
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365 def new() |
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366 this.myID = Vehicle.GetID() |
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367 enddef |
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368 endclass |
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369 < |
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370 Class variables and methods are not inherited by a child class. A child class |
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371 can declare a static variable or a method with the same name as the one in the |
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372 super class. Depending on the class where the member is used the |
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373 corresponding class member will be used. The type of the class member in a |
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374 child class can be different from that in the super class. |
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375 |
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376 The double underscore (__) prefix for a class or object method name is |
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377 reserved for future use. |
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378 |
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379 *object-final-variable* *E1409* |
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380 The |:final| keyword can be used to make a class or object variable a |
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381 constant. Examples: > |
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382 |
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383 class A |
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384 final v1 = [1, 2] # final object variable |
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385 public final v2 = {x: 1} # final object variable |
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386 static final v3 = 'abc' # final class variable |
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387 public static final v4 = 0z10 # final class variable |
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388 endclass |
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389 < |
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390 A final variable can be changed only from a constructor function. Example: > |
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391 |
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392 class A |
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393 final v1: list<number> |
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394 def new() |
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395 this.v1 = [1, 2] |
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396 enddef |
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397 endclass |
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398 var a = A.new() |
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399 echo a.v1 |
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400 < |
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401 Note that the value of a final variable can be changed. Example: > |
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402 |
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403 class A |
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404 public final v1 = [1, 2] |
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405 endclass |
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406 var a = A.new() |
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407 a.v1[0] = 6 # OK |
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408 a.v1->add(3) # OK |
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409 a.v1 = [3, 4] # Error |
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410 < |
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411 *E1408* |
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412 Final variables are not supported in an interface. A class or object method |
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413 cannot be final. |
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414 |
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415 *object-const-variable* |
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416 The |:const| keyword can be used to make a class or object variable and the |
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417 value a constant. Examples: > |
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418 |
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419 class A |
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420 const v1 = [1, 2] # const object variable |
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421 public const v2 = {x: 1} # const object variable |
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422 static const v3 = 'abc' # const class variable |
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423 public static const v4 = 0z10 # const class variable |
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424 endclass |
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425 < |
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426 A const variable can be changed only from a constructor function. Example: > |
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427 |
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428 class A |
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429 const v1: list<number> |
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430 def new() |
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431 this.v1 = [1, 2] |
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432 enddef |
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433 endclass |
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434 var a = A.new() |
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435 echo a.v1 |
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436 < |
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437 A const variable and its value cannot be changed. Example: > |
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438 |
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439 class A |
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440 public const v1 = [1, 2] |
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441 endclass |
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442 var a = A.new() |
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443 a.v1[0] = 6 # Error |
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444 a.v1->add(3) # Error |
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445 a.v1 = [3, 4] # Error |
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446 < |
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447 *E1410* |
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448 Const variables are not supported in an interface. A class or object method |
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449 cannot be a const. |
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450 |
31885 | 451 ============================================================================== |
452 | |
453 4. Using an abstract class *Vim9-abstract-class* | |
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454 |
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455 An abstract class forms the base for at least one sub-class. In the class |
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456 model one often finds that a few classes have the same properties that can be |
31885 | 457 shared, but a class with these properties does not have enough state to create |
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458 an object from. A sub-class must extend the abstract class and add the |
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459 missing state and/or methods before it can be used to create objects for. |
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460 |
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461 For example, a Shape class could store a color and thickness. You cannot |
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462 create a Shape object, it is missing the information about what kind of shape |
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463 it is. The Shape class functions as the base for a Square and a Triangle |
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464 class, for which objects can be created. Example: > |
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465 |
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466 abstract class Shape |
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467 var color = Color.Black |
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468 var thickness = 10 |
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469 endclass |
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470 |
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471 class Square extends Shape |
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472 var size: number |
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473 |
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474 def new(this.size) |
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475 enddef |
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476 endclass |
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477 |
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478 class Triangle extends Shape |
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479 var base: number |
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480 var height: number |
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481 |
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482 def new(this.base, this.height) |
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483 enddef |
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484 endclass |
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485 < |
31885 | 486 An abstract class is defined the same way as a normal class, except that it |
487 does not have any new() method. *E1359* | |
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488 |
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489 *abstract-method* *E1371* *E1372* |
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490 An abstract method can be defined in an abstract class by using the "abstract" |
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491 prefix when defining the method: > |
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492 |
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493 abstract class Shape |
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494 abstract def Draw() |
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495 abstract static def SetColor() |
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496 endclass |
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497 < |
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498 A static method in an abstract class cannot be an abstract method. |
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499 |
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500 *E1373* |
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501 A class extending the abstract class must implement all the abstract methods. |
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502 The signature (arguments, argument types and return type) must be exactly the |
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503 same. If the return type of a method is a class, then that class or one of |
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504 its subclasses can be used in the extended method. Class methods in an |
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505 abstract class can also be abstract methods. |
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506 |
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507 ============================================================================== |
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508 |
31885 | 509 5. Using an interface *Vim9-using-interface* |
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510 |
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511 The example above with Shape, Square and Triangle can be made more useful if |
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512 we add a method to compute the surface of the object. For that we create the |
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513 interface called HasSurface, which specifies one method Surface() that returns |
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514 a number. This example extends the one above: > |
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515 |
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516 abstract class Shape |
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517 var color = Color.Black |
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518 var thickness = 10 |
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519 endclass |
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520 |
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521 interface HasSurface |
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522 def Surface(): number |
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523 endinterface |
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524 |
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525 class Square extends Shape implements HasSurface |
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526 var size: number |
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527 |
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528 def new(this.size) |
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529 enddef |
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530 |
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531 def Surface(): number |
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532 return this.size * this.size |
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533 enddef |
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534 endclass |
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535 |
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536 class Triangle extends Shape implements HasSurface |
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537 var base: number |
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538 var height: number |
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539 |
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540 def new(this.base, this.height) |
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541 enddef |
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542 |
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543 def Surface(): number |
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544 return this.base * this.height / 2 |
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545 enddef |
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546 endclass |
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547 < |
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548 *E1348* *E1349* *E1367* *E1382* *E1383* |
31671 | 549 If a class declares to implement an interface, all the items specified in the |
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550 interface must appear in the class, with the same types. |
31671 | 551 |
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552 The interface name can be used as a type: > |
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553 |
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554 var shapes: list<HasSurface> = [ |
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555 Square.new(12), |
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556 Triangle.new(8, 15), |
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557 ] |
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558 for shape in shapes |
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559 echo $'the surface is {shape.Surface()}' |
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560 endfor |
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561 < |
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562 *E1378* *E1379* *E1380* *E1387* |
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563 An interface can contain only object methods and read-only object variables. |
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564 An interface cannot contain read-write or protected object variables, |
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565 protected object methods, class variables and class methods. |
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566 |
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567 An interface can extend another interface using "extends". The sub-interface |
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568 inherits all the instance variables and methods from the super interface. |
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569 |
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570 ============================================================================== |
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571 |
31885 | 572 6. More class details *Vim9-class* *Class* *class* |
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573 |
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574 Defining a class ~ |
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575 *:class* *:endclass* *:abstract* |
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576 A class is defined between `:class` and `:endclass`. The whole class is |
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577 defined in one script file. It is not possible to add to a class later. |
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578 |
31430 | 579 A class can only be defined in a |Vim9| script file. *E1316* |
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580 A class cannot be defined inside a function. |
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581 |
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582 It is possible to define more than one class in a script file. Although it |
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583 usually is better to export only one main class. It can be useful to define |
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584 types, enums and helper classes though. |
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585 |
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586 The `:abstract` keyword may be prefixed and `:export` may be used. That gives |
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587 these variants: > |
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588 |
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589 class ClassName |
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590 endclass |
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591 |
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592 export class ClassName |
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593 endclass |
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594 |
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595 abstract class ClassName |
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596 endclass |
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597 |
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598 export abstract class ClassName |
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599 endclass |
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600 < |
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601 *E1314* |
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602 The class name should be CamelCased. It must start with an uppercase letter. |
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603 That avoids clashing with builtin types. |
31430 | 604 *E1315* |
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605 After the class name these optional items can be used. Each can appear only |
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606 once. They can appear in any order, although this order is recommended: > |
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607 extends ClassName |
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608 implements InterfaceName, OtherInterface |
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609 specifies SomeInterface |
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610 < *E1355* *E1369* |
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611 Each variable and method name can be used only once. It is not possible to |
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612 define a method with the same name and different type of arguments. It is not |
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613 possible to use a public and protected member variable with the same name. A |
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614 object variable name used in a super class cannot be reused in a child class. |
31885 | 615 |
616 | |
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617 Object Variable Initialization ~ |
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618 |
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619 If the type of a variable is not explicitly specified in a class, then it is |
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620 set to "any" during class definition. When an object is instantiated from the |
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621 class, then the type of the variable is set. |
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622 |
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623 The following reserved keyword names cannot be used as an object or class |
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624 variable name: "super", "this", "true", "false", "null", "null_blob", |
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625 "null_dict", "null_function", "null_list", "null_partial", "null_string", |
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626 "null_channel" and "null_job". |
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627 |
31885 | 628 Extending a class ~ |
629 *extends* | |
31671 | 630 A class can extend one other class. *E1352* *E1353* *E1354* |
31885 | 631 The basic idea is to build on top of an existing class, add properties to it. |
632 | |
633 The extended class is called the "base class" or "super class". The new class | |
634 is called the "child class". | |
635 | |
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636 Object variables from the base class are all taken over by the child class. It |
31885 | 637 is not possible to override them (unlike some other languages). |
638 | |
639 *E1356* *E1357* *E1358* | |
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640 Object methods of the base class can be overruled. The signature (arguments, |
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641 argument types and return type) must be exactly the same. If the return type |
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642 of a method is a class, then that class or one of its subclasses can be used |
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643 in the extended method. The method of the base class can be called by |
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644 prefixing "super.". |
31885 | 645 |
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646 *E1377* |
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647 The access level of a method (public or protected) in a child class should be |
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648 the same as the super class. |
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649 |
31885 | 650 Other object methods of the base class are taken over by the child class. |
651 | |
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652 Class methods, including methods starting with "new", can be overruled, like |
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653 with object methods. The method on the base class can be called by prefixing |
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654 the name of the class (for class methods) or "super.". |
31885 | 655 |
656 Unlike other languages, the constructor of the base class does not need to be | |
657 invoked. In fact, it cannot be invoked. If some initialization from the base | |
658 class also needs to be done in a child class, put it in an object method and | |
659 call that method from every constructor(). | |
660 | |
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661 If the base class did not specify a new() method then one was automatically |
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662 created. This method will not be taken over by the child class. The child |
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663 class can define its own new() method, or, if there isn't one, a new() method |
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664 will be added automatically. |
31885 | 665 |
666 | |
667 A class implementing an interface ~ | |
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668 *implements* *E1346* *E1347* *E1389* |
31671 | 669 A class can implement one or more interfaces. The "implements" keyword can |
670 only appear once *E1350* . Multiple interfaces can be specified, separated by | |
671 commas. Each interface name can appear only once. *E1351* | |
31885 | 672 |
673 | |
674 A class defining an interface ~ | |
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675 *specifies* |
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676 A class can declare its interface, the object variables and methods, with a |
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677 named interface. This avoids the need for separately specifying the |
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678 interface, which is often done in many languages, especially Java. |
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679 |
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680 |
31430 | 681 Items in a class ~ |
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682 *E1318* *E1325* *E1388* |
32061 | 683 Inside a class, in between `:class` and `:endclass`, these items can appear: |
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684 - An object variable declaration: > |
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685 var _protectedVariableName: memberType |
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686 var readonlyVariableName: memberType |
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687 public var readwriteVariableName: memberType |
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688 - A class variable declaration: > |
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689 static var _protectedClassVariableName: memberType |
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690 static var readonlyClassVariableName: memberType |
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691 static var public readwriteClassVariableName: memberType |
31430 | 692 - A constructor method: > |
32004 | 693 def new(arguments) |
694 def newName(arguments) | |
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695 - A class method: > |
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696 static def SomeMethod(arguments) |
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697 static def _ProtectedMethod(arguments) |
31430 | 698 - An object method: > |
32004 | 699 def SomeMethod(arguments) |
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700 def _ProtectedMethod(arguments) |
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701 |
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702 For the object variable the type must be specified. The best way is to do |
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703 this explicitly with ": {type}". For simple types you can also use an |
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704 initializer, such as "= 123", and Vim will see that the type is a number. |
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705 Avoid doing this for more complex types and when the type will be incomplete. |
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706 For example: > |
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707 var nameList = [] |
31579 | 708 This specifies a list, but the item type is unknown. Better use: > |
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709 var nameList: list<string> |
31579 | 710 The initialization isn't needed, the list is empty by default. |
711 *E1330* | |
712 Some types cannot be used, such as "void", "null" and "v:none". | |
31430 | 713 |
714 | |
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715 Defining an interface ~ |
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716 *:interface* *:endinterface* |
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717 An interface is defined between `:interface` and `:endinterface`. It may be |
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718 prefixed with `:export`: > |
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719 |
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720 interface InterfaceName |
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721 endinterface |
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722 |
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723 export interface InterfaceName |
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724 endinterface |
31671 | 725 < *E1344* |
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726 An interface can declare object variables, just like in a class but without |
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727 any initializer. |
31671 | 728 *E1345* |
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729 An interface can declare methods with `:def`, including the arguments and |
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730 return type, but without the body and without `:enddef`. Example: > |
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731 |
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|
732 interface HasSurface |
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733 var size: number |
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734 def Surface(): number |
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735 endinterface |
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736 |
31671 | 737 An interface name must start with an uppercase letter. *E1343* |
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738 The "Has" prefix can be used to make it easier to guess this is an interface |
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739 name, with a hint about what it provides. |
31671 | 740 An interface can only be defined in a |Vim9| script file. *E1342* |
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741 An interface cannot "implement" another interface but it can "extend" another |
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742 interface. *E1381* |
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743 |
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744 |
32004 | 745 null object ~ |
746 | |
32061 | 747 When a variable is declared to have the type of an object, but it is not |
32004 | 748 initialized, the value is null. When trying to use this null object Vim often |
749 does not know what class was supposed to be used. Vim then cannot check if | |
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750 a variable name is correct and you will get an "Using a null object" error, |
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751 even when the variable name is invalid. *E1360* *E1362* |
32004 | 752 |
753 | |
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754 Default constructor ~ |
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755 *default-constructor* |
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756 In case you define a class without a new() method, one will be automatically |
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757 defined. This default constructor will have arguments for all the object |
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758 variables, in the order they were specified. Thus if your class looks like: > |
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759 |
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760 class AutoNew |
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761 var name: string |
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762 var age: number |
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763 var gender: Gender |
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764 endclass |
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765 |
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766 Then the default constructor will be: > |
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767 |
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768 def new(this.name = v:none, this.age = v:none, this.gender = v:none) |
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769 enddef |
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770 |
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771 The "= v:none" default values make the arguments optional. Thus you can also |
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772 call `new()` without any arguments. No assignment will happen and the default |
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773 value for the object variables will be used. This is a more useful example, |
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774 with default values: > |
31430 | 775 |
776 class TextPosition | |
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777 var lnum: number = 1 |
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778 var col: number = 1 |
31430 | 779 endclass |
780 | |
781 If you want the constructor to have mandatory arguments, you need to write it | |
782 yourself. For example, if for the AutoNew class above you insist on getting | |
783 the name, you can define the constructor like this: > | |
784 | |
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785 def new(this.name, this.age = v:none, this.gender = v:none) |
31430 | 786 enddef |
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787 < |
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788 When using the default new() method, if the order of the object variables in |
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789 the class is changed later, then all the callers of the default new() method |
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790 needs to change. To avoid this, the new() method can be explicitly defined |
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791 without any arguments. |
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792 |
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793 *E1328* |
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794 Note that you cannot use another default value than "v:none" here. If you |
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795 want to initialize the object variables, do it where they are declared. This |
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796 way you only need to look in one place for the default values. |
31430 | 797 |
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798 All object variables will be used in the default constructor, including |
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799 protected access ones. |
31671 | 800 |
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801 If the class extends another one, the object variables of that class will come |
31671 | 802 first. |
803 | |
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804 |
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805 Multiple constructors ~ |
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806 *multiple-constructors* |
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807 Normally a class has just one new() constructor. In case you find that the |
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808 constructor is often called with the same arguments you may want to simplify |
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809 your code by putting those arguments into a second constructor method. For |
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810 example, if you tend to use the color black a lot: > |
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811 |
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812 def new(this.garment, this.color, this.size) |
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813 enddef |
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814 ... |
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815 var pants = new(Garment.pants, Color.black, "XL") |
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816 var shirt = new(Garment.shirt, Color.black, "XL") |
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817 var shoes = new(Garment.shoes, Color.black, "45") |
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818 |
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819 Instead of repeating the color every time you can add a constructor that |
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820 includes it: > |
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821 |
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822 def newBlack(this.garment, this.size) |
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823 this.color = Color.black |
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824 enddef |
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825 ... |
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826 var pants = newBlack(Garment.pants, "XL") |
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827 var shirt = newBlack(Garment.shirt, "XL") |
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828 var shoes = newBlack(Garment.shoes, "9.5") |
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829 |
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830 Note that the method name must start with "new". If there is no method called |
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831 "new()" then the default constructor is added, even though there are other |
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832 constructor methods. |
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833 |
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834 |
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835 ============================================================================== |
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836 |
31885 | 837 7. Type definition *Vim9-type* *:type* |
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838 |
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839 *E1393* *E1395* *E1396* *E1397* *E1398* |
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840 A type definition is giving a name to a type specification. This is also |
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841 known as a "type alias". The type alias can be used wherever a built-in type |
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842 can be used. Example: > |
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843 |
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844 type ListOfStrings = list<string> |
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845 var s: ListOfStrings = ['a', 'b'] |
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846 |
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847 def ProcessStr(str: ListOfStrings): ListOfStrings |
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848 return str |
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849 enddef |
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850 echo ProcessStr(s) |
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851 < |
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852 *E1394* |
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853 A type alias name must start with an upper case character. Only existing |
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854 types can be aliased. |
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855 |
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856 *E1399* |
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857 A type alias can be created only at the script level and not inside a |
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858 function. A type alias can be exported and used across scripts. |
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859 |
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860 *E1400* *E1401* *E1402* *E1403* *E1407* |
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861 A type alias cannot be used as an expression. A type alias cannot be used in |
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862 the left-hand-side of an assignment. |
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863 |
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864 For a type alias name, the |typename()| function returns the type that is |
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865 aliased: > |
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866 |
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867 type ListOfStudents = list<dict<any>> |
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868 echo typename(ListOfStudents) |
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869 typealias<list<dict<any>>> |
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870 < |
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871 ============================================================================== |
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872 |
31885 | 873 8. Enum *Vim9-enum* *:enum* *:endenum* |
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874 |
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875 {not implemented yet} |
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876 |
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877 An enum is a type that can have one of a list of values. Example: > |
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878 |
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879 :enum Color |
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880 White |
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881 Red |
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882 Green |
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883 Blue |
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884 Black |
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885 :endenum |
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886 |
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887 |
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888 ============================================================================== |
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889 |
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890 9. Rationale |
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891 |
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892 Most of the choices for |Vim9| classes come from popular and recently |
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893 developed languages, such as Java, TypeScript and Dart. The syntax has been |
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894 made to fit with the way Vim script works, such as using `endclass` instead of |
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895 using curly braces around the whole class. |
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896 |
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897 Some common constructs of object-oriented languages were chosen very long ago |
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898 when this kind of programming was still new, and later found to be |
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899 sub-optimal. By this time those constructs were widely used and changing them |
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900 was not an option. In Vim we do have the freedom to make different choices, |
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901 since classes are completely new. We can make the syntax simpler and more |
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902 consistent than what "old" languages use. Without diverting too much, it |
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903 should still mostly look like what you know from existing languages. |
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904 |
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905 Some recently developed languages add all kinds of fancy features that we |
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906 don't need for Vim. But some have nice ideas that we do want to use. |
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907 Thus we end up with a base of what is common in popular languages, dropping |
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908 what looks like a bad idea, and adding some nice features that are easy to |
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909 understand. |
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910 |
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911 The main rules we use to make decisions: |
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912 - Keep it simple. |
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913 - No surprises, mostly do what other languages are doing. |
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914 - Avoid mistakes from the past. |
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915 - Avoid the need for the script writer to consult the help to understand how |
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916 things work, most things should be obvious. |
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917 - Keep it consistent. |
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918 - Aim at an average size plugin, not at a huge project. |
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919 |
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920 |
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921 Using new() for the constructor ~ |
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922 |
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923 Many languages use the class name for the constructor method. A disadvantage |
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924 is that quite often this is a long name. And when changing the class name all |
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925 constructor methods need to be renamed. Not a big deal, but still a |
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926 disadvantage. |
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927 |
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928 Other languages, such as TypeScript, use a specific name, such as |
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929 "constructor()". That seems better. However, using "new" or "new()" to |
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930 create a new object has no obvious relation with "constructor()". |
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931 |
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932 For |Vim9| script using the same method name for all constructors seemed like |
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933 the right choice, and by calling it new() the relation between the caller and |
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934 the method being called is obvious. |
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935 |
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936 |
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937 No overloading of the constructor ~ |
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938 |
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939 In Vim script, both legacy and |Vim9| script, there is no overloading of |
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940 methods. That means it is not possible to use the same method name with |
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941 different types of arguments. Therefore there also is only one new() |
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942 constructor. |
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943 |
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944 With |Vim9| script it would be possible to support overloading, since |
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945 arguments are typed. However, this gets complicated very quickly. Looking at |
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946 a new() call one has to inspect the types of the arguments to know which of |
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947 several new() methods is actually being called. And that can require |
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948 inspecting quite a bit of code. For example, if one of the arguments is the |
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949 return value of a method, you need to find that method to see what type it is |
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950 returning. |
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951 |
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952 Instead, every constructor has to have a different name, starting with "new". |
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953 That way multiple constructors with different arguments are possible, while it |
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954 is very easy to see which constructor is being used. And the type of |
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955 arguments can be properly checked. |
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956 |
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957 |
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958 No overloading of methods ~ |
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959 |
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960 Same reasoning as for the constructor: It is often not obvious what type |
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961 arguments have, which would make it difficult to figure out what method is |
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962 actually being called. Better just give the methods a different name, then |
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963 type checking will make sure it works as you intended. This rules out |
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964 polymorphism, which we don't really need anyway. |
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965 |
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966 |
31671 | 967 Single inheritance and interfaces ~ |
968 | |
969 Some languages support multiple inheritance. Although that can be useful in | |
970 some cases, it makes the rules of how a class works quite complicated. | |
971 Instead, using interfaces to declare what is supported is much simpler. The | |
972 very popular Java language does it this way, and it should be good enough for | |
31885 | 973 Vim. The "keep it simple" rule applies here. |
31671 | 974 |
975 Explicitly declaring that a class supports an interface makes it easy to see | |
976 what a class is intended for. It also makes it possible to do proper type | |
977 checking. When an interface is changed any class that declares to implement | |
978 it will be checked if that change was also changed. The mechanism to assume a | |
979 class implements an interface just because the methods happen to match is | |
980 brittle and leads to obscure problems, let's not do that. | |
981 | |
982 | |
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983 Using "this.variable" everywhere ~ |
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984 |
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985 The object variables in various programming languages can often be accessed in |
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986 different ways, depending on the location. Sometimes "this." has to be |
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987 prepended to avoid ambiguity. They are usually declared without "this.". |
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988 That is quite inconsistent and sometimes confusing. |
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989 |
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990 A very common issue is that in the constructor the arguments use the same name |
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991 as the object variable. Then for these variables "this." needs to be prefixed |
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992 in the body, while for other variables this is not needed and often omitted. |
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993 This leads to a mix of variables with and without "this.", which is |
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994 inconsistent. |
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995 |
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996 For |Vim9| classes the "this." prefix is always used. Also for declaring the |
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997 variables. Simple and consistent. When looking at the code inside a class |
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998 it's also directly clear which variable references are object variables and |
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999 which aren't. |
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1000 |
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1001 |
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1002 Using class variables ~ |
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1003 |
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1004 Using "static variable" to declare a class variable is very common, nothing |
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1005 new here. In |Vim9| script these can be accessed directly by their name. |
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1006 Very much like how a script-local variable can be used in a method. Since |
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1007 object variables are always accessed with "this." prepended, it's also quickly |
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1008 clear what kind of variable it is. |
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1009 |
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1010 TypeScript prepends the class name before the class variable name, also inside |
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1011 the class. This has two problems: The class name can be rather long, taking |
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1012 up quite a bit of space, and when the class is renamed all these places need |
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1013 to be changed too. |
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1014 |
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1015 |
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1016 Declaring object and class variables ~ |
31671 | 1017 |
1018 The main choice is whether to use "var" as with variable declarations. | |
1019 TypeScript does not use it: > | |
1020 class Point { | |
1021 x: number; | |
1022 y = 0; | |
1023 } | |
1024 | |
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1025 Following that Vim object variables could be declared like this: > |
31671 | 1026 class Point |
1027 this.x: number | |
1028 this.y = 0 | |
1029 endclass | |
1030 | |
1031 Some users pointed out that this looks more like an assignment than a | |
1032 declaration. Adding "var" changes that: > | |
1033 class Point | |
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1034 var x: number |
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1035 var y = 0 |
31671 | 1036 endclass |
1037 | |
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1038 We also need to be able to declare class variables using the "static" keyword. |
31671 | 1039 There we can also choose to leave out "var": > |
1040 class Point | |
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1041 var x: number |
31671 | 1042 static count = 0 |
1043 endclass | |
1044 | |
1045 Or do use it, before "static": > | |
1046 class Point | |
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1047 var x: number |
31671 | 1048 var static count = 0 |
1049 endclass | |
1050 | |
1051 Or after "static": > | |
1052 class Point | |
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1053 var x: number |
31671 | 1054 static var count = 0 |
1055 endclass | |
1056 | |
1057 This is more in line with "static def Func()". | |
1058 | |
1059 There is no clear preference whether to use "var" or not. The two main | |
1060 reasons to leave it out are: | |
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1061 1. TypeScript and other popular languages do not use it. |
31671 | 1062 2. Less clutter. |
1063 | |
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1064 However, it is more common for languages to reuse their general variable and |
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1065 function declaration syntax for class/object variables and methods. Vim9 also |
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1066 reuses the general function declaration syntax for methods. So, for the sake |
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1067 of consistency, we require "var" in these declarations. |
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1068 |
31671 | 1069 |
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1070 Using "ClassName.new()" to construct an object ~ |
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1071 |
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1072 Many languages use the "new" operator to create an object, which is actually |
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1073 kind of strange, since the constructor is defined as a method with arguments, |
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1074 not a command. TypeScript also has the "new" keyword, but the method is |
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1075 called "constructor()", it is hard to see the relation between the two. |
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1076 |
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1077 In |Vim9| script the constructor method is called new(), and it is invoked as |
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1078 new(), simple and straightforward. Other languages use "new ClassName()", |
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1079 while there is no ClassName() method, it's a method by another name in the |
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1080 class called ClassName. Quite confusing. |
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1081 |
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1082 |
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1083 Vim9class access modes ~ |
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1084 *vim9-access-modes* |
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1085 The variable access modes, and their meaning, supported by Vim9class are |
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1086 |public-variable| read and write from anywhere |
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1087 |read-only-variable| read from anywhere, write from inside the |
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1088 class and sub-classes |
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1089 |protected-variable| read and write from inside the class and |
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1090 sub-classes |
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1091 |
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1092 The method access modes are similar, but without the read-only mode. |
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1093 |
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1094 |
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1095 Default read access to object variables ~ |
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1096 |
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1097 Some users will remark that the access rules for object variables are |
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1098 asymmetric. Well, that is intentional. Changing a value is a very different |
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1099 action than reading a value. The read operation has no side effects, it can |
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1100 be done any number of times without affecting the object. Changing the value |
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1101 can have many side effects, and even have a ripple effect, affecting other |
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1102 objects. |
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1103 |
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1104 When adding object variables one usually doesn't think much about this, just |
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1105 get the type right. And normally the values are set in the new() method. |
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1106 Therefore defaulting to read access only "just works" in most cases. And when |
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1107 directly writing you get an error, which makes you wonder if you actually want |
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1108 to allow that. This helps writing code with fewer mistakes. |
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1109 |
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1110 |
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1111 Making object variables protected with an underscore ~ |
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1112 |
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1113 When an object variable is protected, it can only be read and changed inside |
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1114 the class (and in sub-classes), then it cannot be used outside of the class. |
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1115 Prepending an underscore is a simple way to make that visible. Various |
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1116 programming languages have this as a recommendation. |
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1117 |
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1118 In case you change your mind and want to make the object variable accessible |
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1119 outside of the class, you will have to remove the underscore everywhere. |
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1120 Since the name only appears in the class (and sub-classes) they will be easy |
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1121 to find and change. |
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1122 |
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1123 The other way around is much harder: you can easily prepend an underscore to |
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1124 the object variable inside the class to make it protected, but any usage |
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1125 elsewhere you will have to track down and change. You may have to make it a |
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1126 "set" method call. This reflects the real world problem that taking away |
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1127 access requires work to be done for all places where that access exists. |
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1128 |
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1129 An alternative would have been using the "protected" keyword, just like |
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1130 "public" changes the access in the other direction. Well, that's just to |
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1131 reduce the number of keywords. |
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1132 |
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1133 |
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1134 No private object variables ~ |
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1135 |
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1136 Some languages provide several ways to control access to object variables. |
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1137 The most known is "protected", and the meaning varies from language to |
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1138 language. Others are "shared", "private", "package" and even "friend". |
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1139 |
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1140 These rules make life more difficult. That can be justified in projects where |
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1141 many people work on the same, complex code where it is easy to make mistakes. |
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1142 Especially when refactoring or other changes to the class model. |
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1143 |
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1144 The Vim scripts are expected to be used in a plugin, with just one person or a |
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1145 small team working on it. Complex rules then only make it more complicated, |
32294 | 1146 the extra safety provided by the rules isn't really needed. Let's just keep |
1147 it simple and not specify access details. | |
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1148 |
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1149 |
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1150 ============================================================================== |
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1151 |
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1152 10. To be done later |
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1153 |
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1154 Can a newSomething() constructor invoke another constructor? If yes, what are |
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1155 the restrictions? |
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1156 |
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1157 Thoughts: |
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1158 - Generics for a class: `class <Tkey, Tentry>` |
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1159 - Generics for a function: `def <Tkey> GetLast(key: Tkey)` |
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1160 - Mixins: not sure if that is useful, leave out for simplicity. |
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1161 |
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1162 Some things that look like good additions: |
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1163 - For testing: Mock mechanism |
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1164 |
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1165 An important class to be provided is "Promise". Since Vim is single |
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1166 threaded, connecting asynchronous operations is a natural way of allowing |
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1167 plugins to do their work without blocking the user. It's a uniform way to |
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patch 9.0.1001: classes are not documented or implemented yet
Bram Moolenaar <Bram@vim.org>
parents:
diff
changeset
|
1168 invoke callbacks and handle timeouts and errors. |
5acc0d2cf4f7
patch 9.0.1001: classes are not documented or implemented yet
Bram Moolenaar <Bram@vim.org>
parents:
diff
changeset
|
1169 |
5acc0d2cf4f7
patch 9.0.1001: classes are not documented or implemented yet
Bram Moolenaar <Bram@vim.org>
parents:
diff
changeset
|
1170 |
5acc0d2cf4f7
patch 9.0.1001: classes are not documented or implemented yet
Bram Moolenaar <Bram@vim.org>
parents:
diff
changeset
|
1171 vim:tw=78:ts=8:noet:ft=help:norl: |