Mercurial > vim
annotate runtime/doc/vim9class.txt @ 33942:3bba09502b8d v9.0.2167
patch 9.0.2167: Vim9: not consistently using :var for declarations
Commit: https://github.com/vim/vim/commit/74da0ee0a24799a312a3a8a65858237185ef7a23
Author: Doug Kearns <dougkearns@gmail.com>
Date: Thu Dec 14 20:26:26 2023 +0100
patch 9.0.2167: Vim9: not consistently using :var for declarations
Problem: Vim9-script object/class variable declarations use syntax
that is inconsistent with the rest of the language.
Solution: Use :var to declare object and class variables.
closes: #13670
Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
| author | Christian Brabandt <cb@256bit.org> |
|---|---|
| date | Thu, 14 Dec 2023 20:30:06 +0100 |
| parents | 050160b94f02 |
| children | 27746ed6cb05 |
| rev | line source |
|---|---|
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1 *vim9class.txt* For Vim version 9.0. Last change: 2023 Nov 20 |
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4 VIM REFERENCE MANUAL by Bram Moolenaar |
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5 |
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6 |
| 31885 | 7 NOTE - This is not finished yet, anything can still change! - NOTE |
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8 |
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9 |
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10 Vim9 classes, objects, interfaces, types and enums. |
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11 |
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12 1. Overview |Vim9-class-overview| |
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13 2. A simple class |Vim9-simple-class| |
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14 3. Class variables and methods |Vim9-class-member| |
| 31885 | 15 4. Using an abstract class |Vim9-abstract-class| |
| 16 5. Using an interface |Vim9-using-interface| | |
| 17 6. More class details |Vim9-class| | |
| 18 7. Type definition |Vim9-type| | |
| 19 8. Enum |Vim9-enum| | |
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20 |
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21 9. Rationale |
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22 10. To be done later |
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23 |
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24 ============================================================================== |
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25 |
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26 1. Overview *Vim9-class-overview* |
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27 |
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28 The fancy term is "object-oriented programming". You can find lots of study |
| 31885 | 29 material on this subject. Here we document what |Vim9| script provides, |
| 30 assuming you know the basics already. Added are helpful hints about how to | |
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31 use this functionality effectively. Vim9 classes and objects cannot be used |
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32 in legacy Vim scripts and legacy functions. |
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33 |
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34 The basic item is an object: |
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35 - An object stores state. It contains one or more variables that can each |
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36 have a value. |
| 31885 | 37 - An object provides functions that use and manipulate its state. These |
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38 functions are invoked "on the object", which is what sets it apart from the |
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39 traditional separation of data and code that manipulates the data. |
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40 - An object has a well defined interface, with typed member variables and |
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41 methods. |
| 31885 | 42 - Objects are created from a class and all objects have the same interface. |
| 43 This does not change at runtime, it is not dynamic. | |
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44 |
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45 An object can only be created by a class. A class provides: |
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46 - A new() method, the constructor, which returns an object for the class. |
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47 This method is invoked on the class name: MyClass.new(). |
| 31885 | 48 - State shared by all objects of the class: class variables (class members). |
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49 - A hierarchy of classes, with super-classes and sub-classes, inheritance. |
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50 |
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51 An interface is used to specify properties of an object: |
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52 - An object can declare several interfaces that it implements. |
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53 - Different objects implementing the same interface can be used the same way. |
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54 |
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55 The class hierarchy allows for single inheritance. Otherwise interfaces are |
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56 to be used where needed. |
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57 |
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58 |
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59 Class modeling ~ |
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60 |
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61 You can model classes any way you like. Keep in mind what you are building, |
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62 don't try to model the real world. This can be confusing, especially because |
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63 teachers use real-world objects to explain class relations and you might think |
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64 your model should therefore reflect the real world. It doesn't! The model |
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65 should match your purpose. |
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66 |
| 31885 | 67 Keep in mind that composition (an object contains other objects) is often |
| 68 better than inheritance (an object extends another object). Don't waste time | |
| 69 trying to find the optimal class model. Or waste time discussing whether a | |
| 70 square is a rectangle or that a rectangle is a square. It doesn't matter. | |
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71 |
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72 |
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73 ============================================================================== |
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74 |
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75 2. A simple class *Vim9-simple-class* |
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76 |
| 31885 | 77 Let's start with a simple example: a class that stores a text position (see |
| 78 below for how to do this more efficiently): > | |
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79 |
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80 class TextPosition |
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81 var lnum: number |
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82 var col: number |
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83 |
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84 def new(lnum: number, col: number) |
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85 this.lnum = lnum |
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86 this.col = col |
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87 enddef |
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88 |
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89 def SetLnum(lnum: number) |
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90 this.lnum = lnum |
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91 enddef |
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92 |
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93 def SetCol(col: number) |
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94 this.col = col |
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95 enddef |
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96 |
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97 def SetPosition(lnum: number, col: number) |
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98 this.lnum = lnum |
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99 this.col = col |
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100 enddef |
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101 endclass |
| 31430 | 102 < *object* *Object* |
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103 You can create an object from this class with the new() method: > |
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104 |
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105 var pos = TextPosition.new(1, 1) |
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106 |
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107 The object variables "lnum" and "col" can be accessed directly: > |
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108 |
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109 echo $'The text position is ({pos.lnum}, {pos.col})' |
| 31430 | 110 < *E1317* *E1327* |
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111 If you have been using other object-oriented languages you will notice that |
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112 in Vim the object members are consistently referred to with the "this." |
| 31885 | 113 prefix. This is different from languages like Java and TypeScript. The |
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114 naming convention makes the object members easy to spot. Also, when a |
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115 variable does not have the "this." prefix you know it is not an object |
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116 variable. |
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117 |
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118 |
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119 Object variable write access ~ |
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120 *read-only-variable* |
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121 Now try to change an object variable directly: > |
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122 |
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123 pos.lnum = 9 |
| 31885 | 124 < *E1335* |
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125 This will give you an error! That is because by default object variables can |
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126 be read but not set. That's why the TextPosition class provides a method for |
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127 it: > |
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128 |
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129 pos.SetLnum(9) |
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130 |
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131 Allowing to read but not set an object variable is the most common and safest |
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132 way. Most often there is no problem using a value, while setting a value may |
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133 have side effects that need to be taken care of. In this case, the SetLnum() |
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134 method could check if the line number is valid and either give an error or use |
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135 the closest valid value. |
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136 *:public* *public-variable* *E1331* |
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137 If you don't care about side effects and want to allow the object variable to |
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138 be changed at any time, you can make it public: > |
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139 |
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140 public this.lnum: number |
| 31885 | 141 public this.col: number |
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142 |
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143 Now you don't need the SetLnum(), SetCol() and SetPosition() methods, setting |
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144 "pos.lnum" directly above will no longer give an error. |
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145 *E1326* |
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146 If you try to set an object variable that doesn't exist you get an error: > |
| 31579 | 147 pos.other = 9 |
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148 < E1326: Member not found on object "TextPosition": other ~ |
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149 |
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150 *E1376* |
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151 A object variable cannot be accessed using the class name. |
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152 |
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153 Protected variables ~ |
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154 *protected-variable* *E1332* *E1333* |
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155 On the other hand, if you do not want the object variables to be read directly |
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156 from outside the class or its sub-classes, you can make them protected. This |
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157 is done by prefixing an underscore to the name: > |
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158 |
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159 var _lnum: number |
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160 var _col number |
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161 |
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162 Now you need to provide methods to get the value of the protected variables. |
| 31885 | 163 These are commonly called getters. We recommend using a name that starts with |
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164 "Get": > |
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165 |
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166 def GetLnum(): number |
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167 return this._lnum |
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168 enddef |
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169 |
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170 def GetCol() number |
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171 return this._col |
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172 enddef |
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173 |
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174 This example isn't very useful, the variables might as well have been public. |
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175 It does become useful if you check the value. For example, restrict the line |
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176 number to the total number of lines: > |
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177 |
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178 def GetLnum(): number |
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179 if this._lnum > this._lineCount |
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180 return this._lineCount |
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181 endif |
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182 return this._lnum |
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183 enddef |
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184 < |
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185 Protected methods ~ |
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186 *protected-method* *E1366* |
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187 If you want object methods to be accessible only from other methods of the |
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188 same class and not used from outside the class, then you can make them |
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189 protected. This is done by prefixing the method name with an underscore: > |
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190 |
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191 class SomeClass |
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192 def _Foo(): number |
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193 return 10 |
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194 enddef |
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195 def Bar(): number |
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196 return this._Foo() |
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197 enddef |
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198 endclass |
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199 < |
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200 Accessing a protected method outside the class will result in an error (using |
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201 the above class): > |
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202 |
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203 var a = SomeClass.new() |
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204 a._Foo() |
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205 < |
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206 Simplifying the new() method ~ |
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207 *new()* *constructor* |
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208 Many constructors take values for the object variables. Thus you very often |
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209 see this pattern: > |
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210 |
| 31885 | 211 class SomeClass |
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212 var lnum: number |
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213 var col: number |
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214 |
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215 def new(lnum: number, col: number) |
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216 this.lnum = lnum |
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217 this.col = col |
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218 enddef |
| 31885 | 219 endclass |
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220 < |
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221 *E1390* |
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222 Not only is this text you need to write, it also has the type of each |
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223 variables twice. Since this is so common a shorter way to write new() is |
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224 provided: > |
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225 |
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226 def new(this.lnum, this.col) |
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227 enddef |
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228 |
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229 The semantics are easy to understand: Providing the object variable name, |
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230 including "this.", as the argument to new() means the value provided in the |
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231 new() call is assigned to that object variable. This mechanism comes from the |
| 31885 | 232 Dart language. |
| 233 | |
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234 Putting together this way of using new() and making the variables public |
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235 results in a much shorter class definition than what we started with: > |
| 31885 | 236 |
| 237 class TextPosition | |
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238 public var lnum: number |
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239 public var col: number |
| 31885 | 240 |
| 241 def new(this.lnum, this.col) | |
| 242 enddef | |
| 243 | |
| 244 def SetPosition(lnum: number, col: number) | |
| 245 this.lnum = lnum | |
| 246 this.col = col | |
| 247 enddef | |
| 248 endclass | |
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249 |
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250 The sequence of constructing a new object is: |
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251 1. Memory is allocated and cleared. All values are zero/false/empty. |
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252 2. For each declared object variable that has an initializer, the expression |
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253 is evaluated and assigned to the variable. This happens in the sequence |
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254 the variables are declared in the class. |
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255 3. Arguments in the new() method in the "this.name" form are assigned. |
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256 4. The body of the new() method is executed. |
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257 |
| 31885 | 258 If the class extends a parent class, the same thing happens. In the second |
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259 step the object variables of the parent class are initialized first. There is |
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260 no need to call "super()" or "new()" on the parent. |
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261 |
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262 *E1365* |
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263 When defining the new() method the return type should not be specified. It |
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264 always returns an object of the class. |
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265 |
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266 *E1386* |
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267 When invoking an object method, the method name should be preceded by the |
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268 object variable name. A object method cannot be invoked using the class |
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269 name. |
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270 |
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271 ============================================================================== |
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272 |
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273 3. Class Variables and Methods *Vim9-class-member* |
| 31885 | 274 |
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275 *:static* *E1337* *E1338* *E1368* |
| 31885 | 276 Class members are declared with "static". They are used by the name without a |
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277 prefix in the class where they are defined: > |
| 31885 | 278 |
| 279 class OtherThing | |
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280 var size: number |
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281 static var totalSize: number |
| 31885 | 282 |
| 283 def new(this.size) | |
| 284 totalSize += this.size | |
| 285 enddef | |
| 286 endclass | |
| 287 < *E1340* *E1341* | |
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288 Since the name is used as-is, shadowing the name by a method argument name |
| 31885 | 289 or local variable name is not allowed. |
| 290 | |
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291 *E1374* *E1375* *E1384* *E1385* |
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292 To access a class member outside of the class where it is defined, the class |
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293 name prefix must be used. A class member cannot be accessed using an object. |
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294 |
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295 Just like object members the access can be made protected by using an |
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296 underscore as the first character in the name, and it can be made public by |
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297 prefixing "public": > |
| 31885 | 298 |
| 299 class OtherThing | |
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300 static var total: number # anybody can read, only class can write |
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301 static var _sum: number # only class can read and write |
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302 public static var result: number # anybody can read and write |
| 31885 | 303 endclass |
| 304 < | |
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305 *class-method* |
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306 Class methods are also declared with "static". They can use the class |
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307 variables but they have no access to the object variables, they cannot use the |
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308 "this" keyword: |
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309 > |
| 31885 | 310 class OtherThing |
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311 var size: number |
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312 static var totalSize: number |
| 31885 | 313 |
| 314 # Clear the total size and return the value it had before. | |
| 315 static def ClearTotalSize(): number | |
| 316 var prev = totalSize | |
| 317 totalSize = 0 | |
| 318 return prev | |
| 319 enddef | |
| 320 endclass | |
| 321 | |
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322 Inside the class the class method can be called by name directly, outside the |
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323 class the class name must be prefixed: `OtherThing.ClearTotalSize()`. To use |
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324 a super class method in a child class, the class name must be prefixed. |
| 31885 | 325 |
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326 Just like object methods the access can be made protected by using an |
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327 underscore as the first character in the method name: > |
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328 |
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329 class OtherThing |
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330 static def _Foo() |
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331 echo "Foo" |
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332 enddef |
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333 def Bar() |
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334 _Foo() |
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335 enddef |
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336 endclass |
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337 < |
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338 *E1370* |
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339 Note that constructors cannot be declared as "static", because they always |
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340 are. |
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341 |
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342 To access the class methods and class variables of a super class in an |
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343 extended class, the class name prefix should be used just as from anywhere |
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344 outside of the defining class: > |
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345 |
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346 vim9script |
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347 class Vehicle |
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348 static var nextID: number = 1000 |
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349 static def GetID(): number |
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350 nextID += 1 |
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351 return nextID |
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352 enddef |
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353 endclass |
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354 class Car extends Vehicle |
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355 var myID: number |
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356 def new() |
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357 this.myID = Vehicle.GetID() |
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358 enddef |
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359 endclass |
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360 < |
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361 Class variables and methods are not inherited by a child class. A child class |
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362 can declare a static variable or a method with the same name as the one in the |
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363 super class. Depending on the class where the member is used the |
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364 corresponding class member will be used. The type of the class member in a |
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365 child class can be different from that in the super class. |
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366 |
| 31885 | 367 ============================================================================== |
| 368 | |
| 369 4. Using an abstract class *Vim9-abstract-class* | |
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370 |
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371 An abstract class forms the base for at least one sub-class. In the class |
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372 model one often finds that a few classes have the same properties that can be |
| 31885 | 373 shared, but a class with these properties does not have enough state to create |
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374 an object from. A sub-class must extend the abstract class and add the |
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375 missing state and/or methods before it can be used to create objects for. |
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376 |
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377 For example, a Shape class could store a color and thickness. You cannot |
|
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378 create a Shape object, it is missing the information about what kind of shape |
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379 it is. The Shape class functions as the base for a Square and a Triangle |
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380 class, for which objects can be created. Example: > |
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381 |
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382 abstract class Shape |
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383 var color = Color.Black |
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384 var thickness = 10 |
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385 endclass |
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386 |
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387 class Square extends Shape |
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388 var size: number |
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389 |
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390 def new(this.size) |
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391 enddef |
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392 endclass |
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393 |
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394 class Triangle extends Shape |
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395 var base: number |
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396 var height: number |
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397 |
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398 def new(this.base, this.height) |
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399 enddef |
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400 endclass |
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401 < |
| 31885 | 402 An abstract class is defined the same way as a normal class, except that it |
| 403 does not have any new() method. *E1359* | |
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404 |
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405 *abstract-method* *E1371* *E1372* |
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406 An abstract method can be defined in an abstract class by using the "abstract" |
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407 prefix when defining the method: > |
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408 |
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409 abstract class Shape |
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410 abstract def Draw() |
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411 abstract static def SetColor() |
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412 endclass |
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413 < |
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414 A static method in an abstract class cannot be an abstract method. |
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415 |
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416 *E1373* |
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417 A class extending the abstract class must implement all the abstract methods. |
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418 The signature (arguments, argument types and return type) must be exactly the |
|
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419 same. If the return type of a method is a class, then that class or one of |
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420 its subclasses can be used in the extended method. Class methods in an |
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421 abstract class can also be abstract methods. |
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422 |
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423 ============================================================================== |
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424 |
| 31885 | 425 5. Using an interface *Vim9-using-interface* |
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426 |
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427 The example above with Shape, Square and Triangle can be made more useful if |
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428 we add a method to compute the surface of the object. For that we create the |
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429 interface called HasSurface, which specifies one method Surface() that returns |
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430 a number. This example extends the one above: > |
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431 |
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432 abstract class Shape |
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433 var color = Color.Black |
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434 var thickness = 10 |
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435 endclass |
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436 |
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437 interface HasSurface |
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438 def Surface(): number |
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439 endinterface |
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440 |
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441 class Square extends Shape implements HasSurface |
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442 var size: number |
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443 |
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444 def new(this.size) |
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445 enddef |
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446 |
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447 def Surface(): number |
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448 return this.size * this.size |
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449 enddef |
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450 endclass |
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451 |
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452 class Triangle extends Shape implements HasSurface |
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453 var base: number |
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454 var height: number |
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455 |
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456 def new(this.base, this.height) |
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457 enddef |
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458 |
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459 def Surface(): number |
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460 return this.base * this.height / 2 |
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461 enddef |
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462 endclass |
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463 < |
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464 *E1348* *E1349* *E1367* *E1382* *E1383* |
| 31671 | 465 If a class declares to implement an interface, all the items specified in the |
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466 interface must appear in the class, with the same types. |
| 31671 | 467 |
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468 The interface name can be used as a type: > |
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469 |
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470 var shapes: list<HasSurface> = [ |
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471 Square.new(12), |
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472 Triangle.new(8, 15), |
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473 ] |
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474 for shape in shapes |
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475 echo $'the surface is {shape.Surface()}' |
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476 endfor |
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477 < |
|
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478 *E1378* *E1379* *E1380* *E1387* |
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479 An interface can contain only object methods and read-only object variables. |
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480 An interface cannot contain read-write or protected object variables, |
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481 protected object methods, class variables and class methods. |
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482 |
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483 An interface can extend another interface using "extends". The sub-interface |
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484 inherits all the instance variables and methods from the super interface. |
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485 |
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486 ============================================================================== |
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487 |
| 31885 | 488 6. More class details *Vim9-class* *Class* *class* |
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489 |
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490 Defining a class ~ |
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491 *:class* *:endclass* *:abstract* |
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492 A class is defined between `:class` and `:endclass`. The whole class is |
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493 defined in one script file. It is not possible to add to a class later. |
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494 |
| 31430 | 495 A class can only be defined in a |Vim9| script file. *E1316* |
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496 A class cannot be defined inside a function. |
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497 |
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498 It is possible to define more than one class in a script file. Although it |
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499 usually is better to export only one main class. It can be useful to define |
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500 types, enums and helper classes though. |
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501 |
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502 The `:abstract` keyword may be prefixed and `:export` may be used. That gives |
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503 these variants: > |
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504 |
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505 class ClassName |
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506 endclass |
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507 |
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508 export class ClassName |
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509 endclass |
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510 |
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511 abstract class ClassName |
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512 endclass |
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513 |
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514 export abstract class ClassName |
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515 endclass |
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516 < |
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517 *E1314* |
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518 The class name should be CamelCased. It must start with an uppercase letter. |
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519 That avoids clashing with builtin types. |
| 31430 | 520 *E1315* |
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521 After the class name these optional items can be used. Each can appear only |
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522 once. They can appear in any order, although this order is recommended: > |
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523 extends ClassName |
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524 implements InterfaceName, OtherInterface |
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525 specifies SomeInterface |
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526 < *E1355* *E1369* |
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527 Each variable and method name can be used only once. It is not possible to |
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528 define a method with the same name and different type of arguments. It is not |
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529 possible to use a public and protected member variable with the same name. A |
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530 object variable name used in a super class cannot be reused in a child class. |
| 31885 | 531 |
| 532 | |
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533 Object Variable Initialization ~ |
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534 |
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535 If the type of a variable is not explicitly specified in a class, then it is |
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536 set to "any" during class definition. When an object is instantiated from the |
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537 class, then the type of the variable is set. |
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538 |
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539 The following reserved keyword names cannot be used as an object or class |
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540 variable name: "super", "this", "true", "false", "null", "null_blob", |
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541 "null_dict", "null_function", "null_list", "null_partial", "null_string", |
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542 "null_channel" and "null_job". |
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543 |
| 31885 | 544 Extending a class ~ |
| 545 *extends* | |
| 31671 | 546 A class can extend one other class. *E1352* *E1353* *E1354* |
| 31885 | 547 The basic idea is to build on top of an existing class, add properties to it. |
| 548 | |
| 549 The extended class is called the "base class" or "super class". The new class | |
| 550 is called the "child class". | |
| 551 | |
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552 Object variables from the base class are all taken over by the child class. It |
| 31885 | 553 is not possible to override them (unlike some other languages). |
| 554 | |
| 555 *E1356* *E1357* *E1358* | |
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556 Object methods of the base class can be overruled. The signature (arguments, |
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557 argument types and return type) must be exactly the same. If the return type |
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558 of a method is a class, then that class or one of its subclasses can be used |
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559 in the extended method. The method of the base class can be called by |
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560 prefixing "super.". |
| 31885 | 561 |
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562 *E1377* |
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563 The access level of a method (public or protected) in a child class should be |
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564 the same as the super class. |
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565 |
| 31885 | 566 Other object methods of the base class are taken over by the child class. |
| 567 | |
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568 Class methods, including methods starting with "new", can be overruled, like |
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569 with object methods. The method on the base class can be called by prefixing |
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570 the name of the class (for class methods) or "super.". |
| 31885 | 571 |
| 572 Unlike other languages, the constructor of the base class does not need to be | |
| 573 invoked. In fact, it cannot be invoked. If some initialization from the base | |
| 574 class also needs to be done in a child class, put it in an object method and | |
| 575 call that method from every constructor(). | |
| 576 | |
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577 If the base class did not specify a new() method then one was automatically |
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578 created. This method will not be taken over by the child class. The child |
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579 class can define its own new() method, or, if there isn't one, a new() method |
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580 will be added automatically. |
| 31885 | 581 |
| 582 | |
| 583 A class implementing an interface ~ | |
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584 *implements* *E1346* *E1347* *E1389* |
| 31671 | 585 A class can implement one or more interfaces. The "implements" keyword can |
| 586 only appear once *E1350* . Multiple interfaces can be specified, separated by | |
| 587 commas. Each interface name can appear only once. *E1351* | |
| 31885 | 588 |
| 589 | |
| 590 A class defining an interface ~ | |
|
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591 *specifies* |
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592 A class can declare its interface, the object variables and methods, with a |
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593 named interface. This avoids the need for separately specifying the |
|
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594 interface, which is often done in many languages, especially Java. |
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595 |
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596 |
| 31430 | 597 Items in a class ~ |
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598 *E1318* *E1325* *E1388* |
| 32061 | 599 Inside a class, in between `:class` and `:endclass`, these items can appear: |
|
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600 - An object variable declaration: > |
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601 var _protectedVariableName: memberType |
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602 var readonlyVariableName: memberType |
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603 public var readwriteVariableName: memberType |
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604 - A class variable declaration: > |
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605 static var _protectedClassVariableName: memberType |
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606 static var readonlyClassVariableName: memberType |
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607 static var public readwriteClassVariableName: memberType |
| 31430 | 608 - A constructor method: > |
| 32004 | 609 def new(arguments) |
| 610 def newName(arguments) | |
|
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611 - A class method: > |
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612 static def SomeMethod(arguments) |
|
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613 static def _ProtectedMethod(arguments) |
| 31430 | 614 - An object method: > |
| 32004 | 615 def SomeMethod(arguments) |
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616 def _ProtectedMethod(arguments) |
|
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617 |
|
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618 For the object variable the type must be specified. The best way is to do |
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619 this explicitly with ": {type}". For simple types you can also use an |
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620 initializer, such as "= 123", and Vim will see that the type is a number. |
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621 Avoid doing this for more complex types and when the type will be incomplete. |
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622 For example: > |
|
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623 var nameList = [] |
| 31579 | 624 This specifies a list, but the item type is unknown. Better use: > |
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625 var nameList: list<string> |
| 31579 | 626 The initialization isn't needed, the list is empty by default. |
| 627 *E1330* | |
| 628 Some types cannot be used, such as "void", "null" and "v:none". | |
| 31430 | 629 |
| 630 | |
|
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631 Defining an interface ~ |
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632 *:interface* *:endinterface* |
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633 An interface is defined between `:interface` and `:endinterface`. It may be |
|
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634 prefixed with `:export`: > |
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635 |
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636 interface InterfaceName |
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637 endinterface |
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638 |
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639 export interface InterfaceName |
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640 endinterface |
| 31671 | 641 < *E1344* |
|
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642 An interface can declare object variables, just like in a class but without |
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643 any initializer. |
| 31671 | 644 *E1345* |
|
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645 An interface can declare methods with `:def`, including the arguments and |
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646 return type, but without the body and without `:enddef`. Example: > |
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647 |
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648 interface HasSurface |
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649 var size: number |
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650 def Surface(): number |
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651 endinterface |
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652 |
| 31671 | 653 An interface name must start with an uppercase letter. *E1343* |
|
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654 The "Has" prefix can be used to make it easier to guess this is an interface |
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655 name, with a hint about what it provides. |
| 31671 | 656 An interface can only be defined in a |Vim9| script file. *E1342* |
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657 An interface cannot "implement" another interface but it can "extend" another |
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658 interface. *E1381* |
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659 |
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660 |
| 32004 | 661 null object ~ |
| 662 | |
| 32061 | 663 When a variable is declared to have the type of an object, but it is not |
| 32004 | 664 initialized, the value is null. When trying to use this null object Vim often |
| 665 does not know what class was supposed to be used. Vim then cannot check if | |
|
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666 a variable name is correct and you will get an "Using a null object" error, |
|
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667 even when the variable name is invalid. *E1360* *E1362* |
| 32004 | 668 |
| 669 | |
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670 Default constructor ~ |
|
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671 *default-constructor* |
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672 In case you define a class without a new() method, one will be automatically |
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673 defined. This default constructor will have arguments for all the object |
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674 variables, in the order they were specified. Thus if your class looks like: > |
|
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675 |
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676 class AutoNew |
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677 var name: string |
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678 var age: number |
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679 var gender: Gender |
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680 endclass |
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681 |
|
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682 Then the default constructor will be: > |
|
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683 |
|
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684 def new(this.name = v:none, this.age = v:none, this.gender = v:none) |
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685 enddef |
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686 |
|
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687 The "= v:none" default values make the arguments optional. Thus you can also |
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688 call `new()` without any arguments. No assignment will happen and the default |
|
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689 value for the object variables will be used. This is a more useful example, |
|
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690 with default values: > |
| 31430 | 691 |
| 692 class TextPosition | |
|
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693 var lnum: number = 1 |
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694 var col: number = 1 |
| 31430 | 695 endclass |
| 696 | |
| 697 If you want the constructor to have mandatory arguments, you need to write it | |
| 698 yourself. For example, if for the AutoNew class above you insist on getting | |
| 699 the name, you can define the constructor like this: > | |
| 700 | |
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701 def new(this.name, this.age = v:none, this.gender = v:none) |
| 31430 | 702 enddef |
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703 < |
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704 When using the default new() method, if the order of the object variables in |
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705 the class is changed later, then all the callers of the default new() method |
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|
706 needs to change. To avoid this, the new() method can be explicitly defined |
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707 without any arguments. |
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|
708 |
|
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|
709 *E1328* |
|
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|
710 Note that you cannot use another default value than "v:none" here. If you |
|
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|
711 want to initialize the object variables, do it where they are declared. This |
|
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|
712 way you only need to look in one place for the default values. |
| 31430 | 713 |
|
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|
714 All object variables will be used in the default constructor, including |
|
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|
715 protected access ones. |
| 31671 | 716 |
|
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|
717 If the class extends another one, the object variables of that class will come |
| 31671 | 718 first. |
| 719 | |
|
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|
720 |
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|
721 Multiple constructors ~ |
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722 |
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|
723 Normally a class has just one new() constructor. In case you find that the |
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724 constructor is often called with the same arguments you may want to simplify |
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|
725 your code by putting those arguments into a second constructor method. For |
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|
726 example, if you tend to use the color black a lot: > |
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|
727 |
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|
728 def new(this.garment, this.color, this.size) |
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729 enddef |
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|
730 ... |
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731 var pants = new(Garment.pants, Color.black, "XL") |
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732 var shirt = new(Garment.shirt, Color.black, "XL") |
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733 var shoes = new(Garment.shoes, Color.black, "45") |
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|
734 |
|
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|
735 Instead of repeating the color every time you can add a constructor that |
|
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|
736 includes it: > |
|
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|
737 |
|
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|
738 def newBlack(this.garment, this.size) |
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|
739 this.color = Color.black |
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740 enddef |
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741 ... |
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|
742 var pants = newBlack(Garment.pants, "XL") |
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|
743 var shirt = newBlack(Garment.shirt, "XL") |
|
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744 var shoes = newBlack(Garment.shoes, "9.5") |
|
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|
745 |
|
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|
746 Note that the method name must start with "new". If there is no method called |
|
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|
747 "new()" then the default constructor is added, even though there are other |
|
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|
748 constructor methods. |
|
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|
749 |
|
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|
750 |
|
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|
751 ============================================================================== |
|
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|
752 |
| 31885 | 753 7. Type definition *Vim9-type* *:type* |
|
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|
754 |
|
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|
755 *E1393* *E1395* *E1396* *E1397* *E1398* |
|
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|
756 A type definition is giving a name to a type specification. This is also |
|
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|
757 known as a "type alias". The type alias can be used wherever a built-in type |
|
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|
758 can be used. Example: > |
|
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|
759 |
|
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|
760 type ListOfStrings = list<string> |
|
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|
761 var s: ListOfStrings = ['a', 'b'] |
|
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762 |
|
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|
763 def ProcessStr(str: ListOfStrings): ListOfStrings |
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764 return str |
|
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|
765 enddef |
|
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|
766 echo ProcessStr(s) |
|
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|
767 < |
|
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|
768 *E1394* |
|
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|
769 A type alias name must start with an upper case character. Only existing |
|
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770 types can be aliased. |
|
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771 |
|
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|
772 *E1399* |
|
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|
773 A type alias can be created only at the script level and not inside a |
|
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|
774 function. A type alias can be exported and used across scripts. |
|
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|
775 |
|
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|
776 *E1400* *E1401* *E1402* *E1403* *E1407* |
|
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|
777 A type alias cannot be used as an expression. A type alias cannot be used in |
|
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|
778 the left-hand-side of an assignment. |
|
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|
779 |
|
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|
780 For a type alias name, the |typename()| function returns the type that is |
|
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|
781 aliased: > |
|
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|
782 |
|
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|
783 type ListOfStudents = list<dict<any>> |
|
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|
784 echo typename(ListOfStudents) |
|
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|
785 typealias<list<dict<any>>> |
|
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|
786 < |
|
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|
787 ============================================================================== |
|
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|
788 |
| 31885 | 789 8. Enum *Vim9-enum* *:enum* *:endenum* |
|
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|
790 |
|
33490
33593174288b
runtime(doc): Update vim9class help (#13292)
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33434
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|
791 {not implemented yet} |
|
33593174288b
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changeset
|
792 |
|
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793 An enum is a type that can have one of a list of values. Example: > |
|
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|
794 |
|
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|
795 :enum Color |
|
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|
796 White |
|
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|
797 Red |
|
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|
798 Green |
|
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|
799 Blue |
|
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|
800 Black |
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|
801 :endenum |
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|
802 |
|
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|
803 |
|
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|
804 ============================================================================== |
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|
805 |
|
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patch 9.0.1001: classes are not documented or implemented yet
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|
806 9. Rationale |
|
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|
807 |
|
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|
808 Most of the choices for |Vim9| classes come from popular and recently |
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|
809 developed languages, such as Java, TypeScript and Dart. The syntax has been |
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810 made to fit with the way Vim script works, such as using `endclass` instead of |
|
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|
811 using curly braces around the whole class. |
|
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|
812 |
|
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|
813 Some common constructs of object-oriented languages were chosen very long ago |
|
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814 when this kind of programming was still new, and later found to be |
|
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|
815 sub-optimal. By this time those constructs were widely used and changing them |
|
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|
816 was not an option. In Vim we do have the freedom to make different choices, |
|
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817 since classes are completely new. We can make the syntax simpler and more |
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818 consistent than what "old" languages use. Without diverting too much, it |
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819 should still mostly look like what you know from existing languages. |
|
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|
820 |
|
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|
821 Some recently developed languages add all kinds of fancy features that we |
|
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|
822 don't need for Vim. But some have nice ideas that we do want to use. |
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823 Thus we end up with a base of what is common in popular languages, dropping |
|
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|
824 what looks like a bad idea, and adding some nice features that are easy to |
|
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|
825 understand. |
|
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|
826 |
|
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|
827 The main rules we use to make decisions: |
|
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|
828 - Keep it simple. |
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829 - No surprises, mostly do what other languages are doing. |
|
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|
830 - Avoid mistakes from the past. |
|
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831 - Avoid the need for the script writer to consult the help to understand how |
|
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|
832 things work, most things should be obvious. |
|
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|
833 - Keep it consistent. |
|
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|
834 - Aim at an average size plugin, not at a huge project. |
|
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|
835 |
|
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|
836 |
|
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|
837 Using new() for the constructor ~ |
|
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|
838 |
|
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|
839 Many languages use the class name for the constructor method. A disadvantage |
|
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840 is that quite often this is a long name. And when changing the class name all |
|
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|
841 constructor methods need to be renamed. Not a big deal, but still a |
|
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|
842 disadvantage. |
|
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|
843 |
|
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parents:
diff
changeset
|
844 Other languages, such as TypeScript, use a specific name, such as |
|
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|
845 "constructor()". That seems better. However, using "new" or "new()" to |
|
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|
846 create a new object has no obvious relation with "constructor()". |
|
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|
847 |
|
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|
848 For |Vim9| script using the same method name for all constructors seemed like |
|
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|
849 the right choice, and by calling it new() the relation between the caller and |
|
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|
850 the method being called is obvious. |
|
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|
851 |
|
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parents:
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changeset
|
852 |
|
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|
853 No overloading of the constructor ~ |
|
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patch 9.0.1001: classes are not documented or implemented yet
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parents:
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|
854 |
|
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patch 9.0.1001: classes are not documented or implemented yet
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parents:
diff
changeset
|
855 In Vim script, both legacy and |Vim9| script, there is no overloading of |
|
33351
a3bbd065fb87
runtime(doc): Vim9: Consistenly use class/object variable and class/object method in help (#13149)
Christian Brabandt <cb@256bit.org>
parents:
33286
diff
changeset
|
856 methods. That means it is not possible to use the same method name with |
|
31335
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parents:
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|
857 different types of arguments. Therefore there also is only one new() |
|
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parents:
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|
858 constructor. |
|
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parents:
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|
859 |
|
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parents:
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|
860 With |Vim9| script it would be possible to support overloading, since |
|
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parents:
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|
861 arguments are typed. However, this gets complicated very quickly. Looking at |
|
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diff
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|
862 a new() call one has to inspect the types of the arguments to know which of |
|
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|
863 several new() methods is actually being called. And that can require |
|
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|
864 inspecting quite a bit of code. For example, if one of the arguments is the |
|
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|
865 return value of a method, you need to find that method to see what type it is |
|
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|
866 returning. |
|
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|
867 |
|
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parents:
diff
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|
868 Instead, every constructor has to have a different name, starting with "new". |
|
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parents:
diff
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|
869 That way multiple constructors with different arguments are possible, while it |
|
5acc0d2cf4f7
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|
870 is very easy to see which constructor is being used. And the type of |
|
5acc0d2cf4f7
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|
871 arguments can be properly checked. |
|
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parents:
diff
changeset
|
872 |
|
5acc0d2cf4f7
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parents:
diff
changeset
|
873 |
|
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874 No overloading of methods ~ |
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875 |
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876 Same reasoning as for the constructor: It is often not obvious what type |
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877 arguments have, which would make it difficult to figure out what method is |
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878 actually being called. Better just give the methods a different name, then |
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879 type checking will make sure it works as you intended. This rules out |
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880 polymorphism, which we don't really need anyway. |
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881 |
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882 |
| 31671 | 883 Single inheritance and interfaces ~ |
| 884 | |
| 885 Some languages support multiple inheritance. Although that can be useful in | |
| 886 some cases, it makes the rules of how a class works quite complicated. | |
| 887 Instead, using interfaces to declare what is supported is much simpler. The | |
| 888 very popular Java language does it this way, and it should be good enough for | |
| 31885 | 889 Vim. The "keep it simple" rule applies here. |
| 31671 | 890 |
| 891 Explicitly declaring that a class supports an interface makes it easy to see | |
| 892 what a class is intended for. It also makes it possible to do proper type | |
| 893 checking. When an interface is changed any class that declares to implement | |
| 894 it will be checked if that change was also changed. The mechanism to assume a | |
| 895 class implements an interface just because the methods happen to match is | |
| 896 brittle and leads to obscure problems, let's not do that. | |
| 897 | |
| 898 | |
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899 Using "this.variable" everywhere ~ |
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900 |
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901 The object variables in various programming languages can often be accessed in |
|
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902 different ways, depending on the location. Sometimes "this." has to be |
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903 prepended to avoid ambiguity. They are usually declared without "this.". |
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904 That is quite inconsistent and sometimes confusing. |
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905 |
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906 A very common issue is that in the constructor the arguments use the same name |
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907 as the object variable. Then for these variables "this." needs to be prefixed |
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908 in the body, while for other variables this is not needed and often omitted. |
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909 This leads to a mix of variables with and without "this.", which is |
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910 inconsistent. |
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911 |
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912 For |Vim9| classes the "this." prefix is always used. Also for declaring the |
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913 variables. Simple and consistent. When looking at the code inside a class |
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914 it's also directly clear which variable references are object variables and |
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915 which aren't. |
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916 |
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917 |
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918 Using class variables ~ |
|
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919 |
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920 Using "static variable" to declare a class variable is very common, nothing |
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921 new here. In |Vim9| script these can be accessed directly by their name. |
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922 Very much like how a script-local variable can be used in a method. Since |
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923 object variables are always accessed with "this." prepended, it's also quickly |
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924 clear what kind of variable it is. |
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925 |
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926 TypeScript prepends the class name before the class variable name, also inside |
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927 the class. This has two problems: The class name can be rather long, taking |
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928 up quite a bit of space, and when the class is renamed all these places need |
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929 to be changed too. |
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930 |
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931 |
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932 Declaring object and class variables ~ |
| 31671 | 933 |
| 934 The main choice is whether to use "var" as with variable declarations. | |
| 935 TypeScript does not use it: > | |
| 936 class Point { | |
| 937 x: number; | |
| 938 y = 0; | |
| 939 } | |
| 940 | |
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941 Following that Vim object variables could be declared like this: > |
| 31671 | 942 class Point |
| 943 this.x: number | |
| 944 this.y = 0 | |
| 945 endclass | |
| 946 | |
| 947 Some users pointed out that this looks more like an assignment than a | |
| 948 declaration. Adding "var" changes that: > | |
| 949 class Point | |
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950 var x: number |
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951 var y = 0 |
| 31671 | 952 endclass |
| 953 | |
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954 We also need to be able to declare class variables using the "static" keyword. |
| 31671 | 955 There we can also choose to leave out "var": > |
| 956 class Point | |
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957 var x: number |
| 31671 | 958 static count = 0 |
| 959 endclass | |
| 960 | |
| 961 Or do use it, before "static": > | |
| 962 class Point | |
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963 var x: number |
| 31671 | 964 var static count = 0 |
| 965 endclass | |
| 966 | |
| 967 Or after "static": > | |
| 968 class Point | |
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969 var x: number |
| 31671 | 970 static var count = 0 |
| 971 endclass | |
| 972 | |
| 973 This is more in line with "static def Func()". | |
| 974 | |
| 975 There is no clear preference whether to use "var" or not. The two main | |
| 976 reasons to leave it out are: | |
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977 1. TypeScript and other popular languages do not use it. |
| 31671 | 978 2. Less clutter. |
| 979 | |
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980 However, it is more common for languages to reuse their general variable and |
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981 function declaration syntax for class/object variables and methods. Vim9 also |
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982 reuses the general function declaration syntax for methods. So, for the sake |
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983 of consistency, we require "var" in these declarations. |
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984 |
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985 This also allows for a natural use of "final" and "const" in the future. |
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986 |
| 31671 | 987 |
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988 Using "ClassName.new()" to construct an object ~ |
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989 |
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990 Many languages use the "new" operator to create an object, which is actually |
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991 kind of strange, since the constructor is defined as a method with arguments, |
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992 not a command. TypeScript also has the "new" keyword, but the method is |
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993 called "constructor()", it is hard to see the relation between the two. |
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994 |
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995 In |Vim9| script the constructor method is called new(), and it is invoked as |
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996 new(), simple and straightforward. Other languages use "new ClassName()", |
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997 while there is no ClassName() method, it's a method by another name in the |
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998 class called ClassName. Quite confusing. |
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999 |
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1000 |
|
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1001 Vim9class access modes ~ |
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1002 *vim9-access-modes* |
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1003 The variable access modes, and their meaning, supported by Vim9class are |
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1004 |public-variable| read and write from anywhere |
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1005 |read-only-variable| read from anywhere, write from inside the |
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1006 class and sub-classes |
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1007 |protected-variable| read and write from inside the class and |
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1008 sub-classes |
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1009 |
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1010 The method access modes are similar, but without the read-only mode. |
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1011 |
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1012 |
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1013 Default read access to object variables ~ |
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1014 |
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1015 Some users will remark that the access rules for object variables are |
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1016 asymmetric. Well, that is intentional. Changing a value is a very different |
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1017 action than reading a value. The read operation has no side effects, it can |
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1018 be done any number of times without affecting the object. Changing the value |
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1019 can have many side effects, and even have a ripple effect, affecting other |
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1020 objects. |
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1021 |
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1022 When adding object variables one usually doesn't think much about this, just |
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1023 get the type right. And normally the values are set in the new() method. |
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1024 Therefore defaulting to read access only "just works" in most cases. And when |
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1025 directly writing you get an error, which makes you wonder if you actually want |
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1026 to allow that. This helps writing code with fewer mistakes. |
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1027 |
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1028 |
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1029 Making object variables protected with an underscore ~ |
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1030 |
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1031 When an object variable is protected, it can only be read and changed inside |
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1032 the class (and in sub-classes), then it cannot be used outside of the class. |
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1033 Prepending an underscore is a simple way to make that visible. Various |
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1034 programming languages have this as a recommendation. |
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1035 |
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1036 In case you change your mind and want to make the object variable accessible |
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1037 outside of the class, you will have to remove the underscore everywhere. |
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1038 Since the name only appears in the class (and sub-classes) they will be easy |
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1039 to find and change. |
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1040 |
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1041 The other way around is much harder: you can easily prepend an underscore to |
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1042 the object variable inside the class to make it protected, but any usage |
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1043 elsewhere you will have to track down and change. You may have to make it a |
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1044 "set" method call. This reflects the real world problem that taking away |
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1045 access requires work to be done for all places where that access exists. |
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1046 |
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1047 An alternative would have been using the "protected" keyword, just like |
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1048 "public" changes the access in the other direction. Well, that's just to |
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1049 reduce the number of keywords. |
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1050 |
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1051 |
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1052 No private object variables ~ |
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1053 |
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1054 Some languages provide several ways to control access to object variables. |
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1055 The most known is "protected", and the meaning varies from language to |
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1056 language. Others are "shared", "private", "package" and even "friend". |
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1057 |
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1058 These rules make life more difficult. That can be justified in projects where |
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1059 many people work on the same, complex code where it is easy to make mistakes. |
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1060 Especially when refactoring or other changes to the class model. |
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1061 |
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1062 The Vim scripts are expected to be used in a plugin, with just one person or a |
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1063 small team working on it. Complex rules then only make it more complicated, |
| 32294 | 1064 the extra safety provided by the rules isn't really needed. Let's just keep |
| 1065 it simple and not specify access details. | |
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1066 |
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1067 |
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1068 ============================================================================== |
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1069 |
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1070 10. To be done later |
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1071 |
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1072 Can a newSomething() constructor invoke another constructor? If yes, what are |
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1073 the restrictions? |
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1074 |
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1075 Thoughts: |
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1076 - Generics for a class: `class <Tkey, Tentry>` |
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1077 - Generics for a function: `def <Tkey> GetLast(key: Tkey)` |
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1078 - Mixins: not sure if that is useful, leave out for simplicity. |
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1079 |
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1080 Some things that look like good additions: |
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1081 - For testing: Mock mechanism |
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1082 |
|
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1083 An important class to be provided is "Promise". Since Vim is single |
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1084 threaded, connecting asynchronous operations is a natural way of allowing |
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1085 plugins to do their work without blocking the user. It's a uniform way to |
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1086 invoke callbacks and handle timeouts and errors. |
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1087 |
|
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1088 |
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1089 vim:tw=78:ts=8:noet:ft=help:norl: |