Mercurial > vim
annotate runtime/doc/vim9class.txt @ 31430:e5e95e8c78a7
Update runtime files
Commit: https://github.com/vim/vim/commit/7db29e4b5c3a347d24ca5062ddaa5cf4c4d54b9c
Author: Bram Moolenaar <Bram@vim.org>
Date: Sun Dec 11 15:53:04 2022 +0000
Update runtime files
author | Bram Moolenaar <Bram@vim.org> |
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date | Sun, 11 Dec 2022 17:00:05 +0100 |
parents | 307f68a41b03 |
children | e572ff386670 |
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31430 | 1 *vim9class.txt* For Vim version 9.0. Last change: 2022 Dec 11 |
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4 VIM REFERENCE MANUAL by Bram Moolenaar |
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7 NOTE - This is under development, anything can still change! - NOTE |
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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. Using an abstract class |Vim9-abstract-class| |
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15 4. Using an interface |Vim9-using-interface| |
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16 5. More class details |Vim9-class| |
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17 6. Type definition |Vim9-type| |
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18 7. Enum |Vim9-enum| |
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19 |
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20 9. Rationale |
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21 10. To be done later |
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22 |
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23 ============================================================================== |
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24 |
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25 1. Overview *Vim9-class-overview* |
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26 |
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27 The fancy term is "object-oriented programming". You can find lots of study |
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28 material about this subject. Here we document what |Vim9| script provides, |
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29 assuming you know the basics already. Added are helpful hints about how |
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30 to use this functionality effectively. |
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31 |
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32 The basic item is an object: |
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33 - An object stores state. It contains one or more variables that can each |
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34 have a value. |
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35 - An object usually provides functions that manipulate its state. These |
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36 functions are invoked "on the object", which is what sets it apart from the |
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37 traditional separation of data and code that manipulates the data. |
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38 - An object has a well defined interface, with typed member variables and |
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39 member functions. |
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40 - Objects are created by a class and all objects have the same interface. |
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41 This never changes, it is not dynamic. |
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42 |
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43 An object can only be created by a class. A class provides: |
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44 - A new() method, the constructor, which returns an object for the class. |
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45 This method is invoked on the class name: MyClass.new(). |
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46 - State shared by all objects of the class: class variables and constants. |
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47 - A hierarchy of classes, with super-classes and sub-classes, inheritance. |
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48 |
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49 An interface is used to specify properties of an object: |
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50 - An object can declare several interfaces that it implements. |
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51 - Different objects implementing the same interface can be used the same way. |
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52 |
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53 The class hierarchy allows for single inheritance. Otherwise interfaces are |
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54 to be used where needed. |
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55 |
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56 |
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57 Class modeling ~ |
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58 |
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59 You can model classes any way you like. Keep in mind what you are building, |
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60 don't try to model the real world. This can be confusing, especially because |
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61 teachers use real-world objects to explain class relations and you might think |
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62 your model should therefore reflect the real world. It doesn't! The model |
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63 should match your purpose. |
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64 |
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65 You will soon find that composition is often better than inheritance. Don't |
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66 waste time trying to find the optimal class model. Or waste time discussing |
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67 whether a square is a rectangle or that a rectangle is a square. It doesn't |
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68 matter. |
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69 |
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70 |
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71 ============================================================================== |
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72 |
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73 2. A simple class *Vim9-simple-class* |
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74 |
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75 Let's start with a simple example: a class that stores a text position: > |
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76 |
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77 class TextPosition |
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78 this.lnum: number |
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79 this.col: number |
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80 |
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81 def new(lnum: number, col: number) |
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82 this.lnum = lnum |
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83 this.col = col |
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84 enddef |
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85 |
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86 def SetLnum(lnum: number) |
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87 this.lnum = lnum |
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88 enddef |
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89 |
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90 def SetCol(col: number) |
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91 this.col = col |
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92 enddef |
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93 |
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94 def SetPosition(lnum: number, col: number) |
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95 this.lnum = lnum |
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96 this.col = col |
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97 enddef |
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98 endclass |
31430 | 99 < *object* *Object* |
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100 You can create an object from this class with the new() method: > |
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101 |
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102 var pos = TextPosition.new(1, 1) |
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103 |
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104 The object members "lnum" and "col" can be accessed directly: > |
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105 |
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106 echo $'The text position is ({pos.lnum}, {pos.col})' |
31430 | 107 < *E1317* *E1327* |
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108 If you have been using other object-oriented languages you will notice that |
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109 in Vim the object members are consistently referred to with the "this." |
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110 prefix. This is different from languages like Java and TypeScript. This |
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111 naming convention makes the object members easy to spot. Also, when a |
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112 variable does not have the "this." prefix you know it is not an object member. |
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113 |
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114 |
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115 Member write access ~ |
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116 |
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117 Now try to change an object member directly: > |
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118 |
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119 pos.lnum = 9 |
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120 |
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121 This will give you an error! That is because by default object members can be |
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122 read but not set. That's why the class provides a method for it: > |
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123 |
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124 pos.SetLnum(9) |
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125 |
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126 Allowing to read but not set an object member is the most common and safest |
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127 way. Most often there is no problem using a value, while setting a value may |
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128 have side effects that need to be taken care of. In this case, the SetLnum() |
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129 method could check if the line number is valid and either give an error or use |
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130 the closest valid value. |
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131 |
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132 If you don't care about side effects and want to allow the object member to be |
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133 changed at any time, you can make it public: > |
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134 |
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135 public this.lnum: number |
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136 public this.col number |
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137 |
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138 Now you don't need the SetLnum(), SetCol() and SetPosition() methods, setting |
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139 "pos.lnum" directly above will no longer give an error. |
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140 |
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141 |
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142 Private members ~ |
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143 |
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144 On the other hand, if you do not want the object members to be read directly, |
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145 you can make them private. This is done by prefixing an underscore to the |
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146 name: > |
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147 |
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148 this._lnum: number |
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149 this._col number |
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150 |
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151 Now you need to provide methods to get the value of the private members. |
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152 These are commonly call getters. We recommend using a name that starts with |
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153 "Get": > |
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154 |
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155 def GetLnum(): number |
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156 return this._lnum |
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157 enddef |
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158 |
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159 def GetCol() number |
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160 return this._col |
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161 enddef |
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162 |
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163 This example isn't very useful, the members might as well have been public. |
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164 It does become useful if you check the value. For example, restrict the line |
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165 number to the total number of lines: > |
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166 |
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167 def GetLnum(): number |
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168 if this._lnum > this._lineCount |
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169 return this._lineCount |
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170 endif |
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171 return this._lnum |
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172 enddef |
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173 |
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174 |
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175 Simplifying the new() method ~ |
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176 |
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177 Many constructors take values for the object members. Thus you very often see |
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178 this pattern: > |
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179 |
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180 this.lnum: number |
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181 this.col: number |
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182 |
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183 def new(lnum: number, col: number) |
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184 this.lnum = lnum |
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185 this.col = col |
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186 enddef |
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187 |
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188 Not only is this text you need to write, it also has the type of each member |
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189 twice. Since this is so common a shorter way to write new() is provided: > |
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190 |
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191 def new(this.lnum, this.col) |
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192 enddef |
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193 |
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194 The semantics are easy to understand: Providing the object member name, |
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195 including "this.", as the argument to new() means the value provided in the |
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196 new() call is assigned to that object member. This mechanism is coming from |
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197 the Dart language. |
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198 |
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199 The sequence of constructing a new object is: |
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200 1. Memory is allocated and cleared. All values are zero/false/empty. |
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201 2. For each declared member that has an initializer, the expression is |
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202 evaluated and assigned to the member. This happens in the sequence the |
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203 members are declared in the class. |
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204 3. Arguments in the new() method in the "this.name" form are assigned. |
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205 4. The body of the new() method is executed. |
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206 |
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207 TODO: for a sub-class the constructor of the parent class will be invoked |
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208 somewhere. |
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209 |
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210 |
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211 ============================================================================== |
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212 |
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213 3. Using an abstract class *Vim9-abstract-class* |
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214 |
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215 An abstract class forms the base for at least one sub-class. In the class |
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216 model one often finds that a few classes have the same properties that can be |
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217 shared, but a class with those properties does not have enough state to create |
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218 an object from. A sub-class must extend the abstract class and add the |
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219 missing state and/or methods before it can be used to create objects for. |
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220 |
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221 An abstract class does not have a new() method. |
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222 |
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223 For example, a Shape class could store a color and thickness. You cannot |
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224 create a Shape object, it is missing the information about what kind of shape |
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225 it is. The Shape class functions as the base for a Square and a Triangle |
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226 class, for which objects can be created. Example: > |
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227 |
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228 abstract class Shape |
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229 this.color = Color.Black |
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230 this.thickness = 10 |
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231 endclass |
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232 |
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233 class Square extends Shape |
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234 this.size: number |
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235 |
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236 def new(this.size) |
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237 enddef |
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238 endclass |
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239 |
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240 class Triangle extends Shape |
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241 this.base: number |
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242 this.height: number |
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243 |
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244 def new(this.base, this.height) |
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245 enddef |
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246 endclass |
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247 < |
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248 *class-member* *:static* |
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249 Class members are declared with "static". They are used by the name without a |
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250 prefix: > |
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251 |
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252 class OtherThing |
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253 this.size: number |
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254 static totalSize: number |
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255 |
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256 def new(this.size) |
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257 totalSize += this.size |
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258 enddef |
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259 endclass |
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260 < |
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261 *class-method* |
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262 Class methods are also declared with "static". They have no access to object |
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263 members, they cannot use the "this" keyword. > |
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264 |
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265 class OtherThing |
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266 this.size: number |
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267 static totalSize: number |
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268 |
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269 " Clear the total size and return the value it had before. |
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270 static def ClearTotalSize(): number |
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271 var prev = totalSize |
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272 totalSize = 0 |
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273 return prev |
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274 enddef |
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275 endclass |
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276 |
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277 |
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278 ============================================================================== |
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279 |
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280 4. Using an interface *Vim9-using-interface* |
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281 |
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282 The example above with Shape, Square and Triangle can be made more useful if |
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283 we add a method to compute the surface of the object. For that we create the |
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284 interface called HasSurface, which specifies one method Surface() that returns |
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285 a number. This example extends the one above: > |
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286 |
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287 abstract class Shape |
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288 this.color = Color.Black |
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289 this.thickness = 10 |
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290 endclass |
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291 |
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292 interface HasSurface |
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293 def Surface(): number |
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294 endinterface |
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295 |
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296 class Square extends Shape implements HasSurface |
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297 this.size: number |
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298 |
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299 def new(this.size) |
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300 enddef |
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301 |
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302 def Surface(): number |
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303 return this.size * this.size |
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304 enddef |
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305 endclass |
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306 |
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307 class Triangle extends Shape implements HasSurface |
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308 this.base: number |
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309 this.height: number |
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310 |
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311 def new(this.base, this.height) |
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312 enddef |
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313 |
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314 def Surface(): number |
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315 return this.base * this.height / 2 |
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316 enddef |
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317 endclass |
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318 |
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319 The interface name can be used as a type: > |
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320 |
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321 var shapes: list<HasSurface> = [ |
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322 Square.new(12), |
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323 Triangle.new(8, 15), |
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324 ] |
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325 for shape in shapes |
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326 echo $'the surface is {shape.Surface()}' |
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327 endfor |
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328 |
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329 |
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330 ============================================================================== |
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331 |
31430 | 332 5. More class details *Vim9-class* *Class* *class* |
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333 |
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334 Defining a class ~ |
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335 *:class* *:endclass* *:abstract* |
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336 A class is defined between `:class` and `:endclass`. The whole class is |
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337 defined in one script file. It is not possible to add to a class later. |
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338 |
31430 | 339 A class can only be defined in a |Vim9| script file. *E1316* |
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340 A class cannot be defined inside a function. |
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341 |
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342 It is possible to define more than one class in a script file. Although it |
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343 usually is better to export only one main class. It can be useful to define |
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344 types, enums and helper classes though. |
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345 |
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346 The `:abstract` keyword may be prefixed and `:export` may be used. That gives |
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347 these variants: > |
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348 |
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349 class ClassName |
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350 endclass |
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351 |
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352 export class ClassName |
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353 endclass |
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354 |
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355 abstract class ClassName |
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356 endclass |
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357 |
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358 export abstract class ClassName |
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359 endclass |
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360 < |
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361 *E1314* |
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362 The class name should be CamelCased. It must start with an uppercase letter. |
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363 That avoids clashing with builtin types. |
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365 After the class name these optional items can be used. Each can appear only |
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366 once. They can appear in any order, although this order is recommended: > |
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367 extends ClassName |
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368 implements InterfaceName, OtherInterface |
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369 specifies SomeInterface |
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370 < *extends* |
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371 A class can extend one other class. |
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372 *implements* |
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373 A class can implement one or more interfaces. |
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374 *specifies* |
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375 A class can declare its interface, the object members and methods, with a |
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376 named interface. This avoids the need for separately specifying the |
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377 interface, which is often done in many languages, especially Java. |
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378 |
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379 |
31430 | 380 Items in a class ~ |
381 *E1318* *E1325* *E1326* | |
382 Inside a class, in betweeen `:class` and `:endclass`, these items can appear: | |
383 - An object member declaration: > | |
384 this._memberName: memberType | |
385 this.memberName: memberType | |
386 public this.memberName: memberType | |
387 - A constructor method: > | |
388 def new(arguments) | |
389 def newName(arguments) | |
390 - An object method: > | |
391 def SomeMethod(arguments) | |
392 | |
393 | |
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394 Defining an interface ~ |
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395 *:interface* *:endinterface* |
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396 An interface is defined between `:interface` and `:endinterface`. It may be |
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397 prefixed with `:export`: > |
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398 |
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399 interface InterfaceName |
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400 endinterface |
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401 |
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402 export interface InterfaceName |
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403 endinterface |
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404 |
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405 An interface can declare object members, just like in a class but without any |
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406 initializer. |
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407 |
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408 An interface can declare methods with `:def`, including the arguments and |
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409 return type, but without the body and without `:enddef`. Example: > |
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410 |
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411 interface HasSurface |
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412 this.size: number |
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413 def Surface(): number |
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414 endinterface |
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415 |
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416 The "Has" prefix can be used to make it easier to guess this is an interface |
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417 name, with a hint about what it provides. |
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418 |
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419 |
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420 Default constructor ~ |
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421 |
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422 In case you define a class without a new() method, one will be automatically |
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423 defined. This default constructor will have arguments for all the object |
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424 members, in the order they were specified. Thus if your class looks like: > |
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425 |
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426 class AutoNew |
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427 this.name: string |
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428 this.age: number |
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429 this.gender: Gender |
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430 endclass |
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431 |
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432 Then The default constructor will be: > |
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433 |
31430 | 434 def new(this.name = void, this.age = void, this.gender = void) |
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435 enddef |
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436 |
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437 All object members will be used, also private access ones. |
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438 |
31430 | 439 The "= void" default values make the arguments optional. Thus you can also |
440 call `new()` without any arguments. Since "void" isn't an actual value, no | |
441 assignment will happen and the default value for the object members will be | |
442 used. This is a more useful example, with default values: > | |
443 | |
444 class TextPosition | |
445 this.lnum: number = 1 | |
446 this.col: number = 1 | |
447 endclass | |
448 | |
449 If you want the constructor to have mandatory arguments, you need to write it | |
450 yourself. For example, if for the AutoNew class above you insist on getting | |
451 the name, you can define the constructor like this: > | |
452 | |
453 def new(this.name, this.age = void, this.gender = void) | |
454 enddef | |
455 | |
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456 |
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457 Multiple constructors ~ |
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458 |
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459 Normally a class has just one new() constructor. In case you find that the |
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460 constructor is often called with the same arguments you may want to simplify |
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461 your code by putting those arguments into a second constructor method. For |
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462 example, if you tend to use the color black a lot: > |
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463 |
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464 def new(this.garment, this.color, this.size) |
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465 enddef |
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466 ... |
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467 var pants = new(Garment.pants, Color.black, "XL") |
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468 var shirt = new(Garment.shirt, Color.black, "XL") |
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469 var shoes = new(Garment.shoes, Color.black, "45") |
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470 |
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471 Instead of repeating the color every time you can add a constructor that |
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472 includes it: > |
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473 |
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474 def newBlack(this.garment, this.size) |
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475 this.color = Color.black |
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476 enddef |
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477 ... |
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478 var pants = newBlack(Garment.pants, "XL") |
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479 var shirt = newBlack(Garment.shirt, "XL") |
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480 var shoes = newBlack(Garment.shoes, "9.5") |
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481 |
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482 Note that the method name must start with "new". If there is no method called |
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483 "new()" then the default constructor is added, even though there are other |
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484 constructor methods. |
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485 |
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486 |
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487 ============================================================================== |
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488 |
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489 6. Type definition *Vim9-type* *:type* |
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490 |
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491 A type definition is giving a name to a type specification. For Example: > |
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492 |
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493 :type ListOfStrings list<string> |
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494 |
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495 TODO: more explanation |
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496 |
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497 |
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498 ============================================================================== |
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499 |
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500 7. Enum *Vim9-enum* *:enum* *:endenum* |
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501 |
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502 An enum is a type that can have one of a list of values. Example: > |
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503 |
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504 :enum Color |
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505 White |
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506 Red |
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507 Green |
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508 Blue |
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509 Black |
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510 :endenum |
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511 |
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512 TODO: more explanation |
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513 |
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514 |
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515 ============================================================================== |
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516 |
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517 9. Rationale |
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518 |
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519 Most of the choices for |Vim9| classes come from popular and recently |
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520 developed languages, such as Java, TypeScript and Dart. The syntax has been |
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521 made to fit with the way Vim script works, such as using `endclass` instead of |
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522 using curly braces around the whole class. |
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523 |
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524 Some common constructs of object-oriented languages were chosen very long ago |
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525 when this kind of programming was still new, and later found to be |
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526 sub-optimal. By this time those constructs were widely used and changing them |
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527 was not an option. In Vim we do have the freedom to make different choices, |
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528 since classes are completely new. We can make the syntax simpler and more |
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529 consistent than what "old" languages use. Without diverting too much, it |
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530 should still mostly look like what you know from existing languages. |
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531 |
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532 Some recently developed languages add all kinds of fancy features that we |
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533 don't need for Vim. But some have nice ideas that we do want to use. |
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534 Thus we end up with a base of what is common in popular languages, dropping |
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535 what looks like a bad idea, and adding some nice features that are easy to |
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536 understand. |
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537 |
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538 The main rules we use to make decisions: |
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539 - Keep it simple. |
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540 - No surprises, mostly do what other languages are doing. |
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541 - Avoid mistakes from the past. |
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542 - Avoid the need for the script writer to consult the help to understand how |
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543 things work, most things should be obvious. |
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544 - Keep it consistent. |
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545 - Aim at an average size plugin, not at a huge project. |
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546 |
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547 |
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548 Using new() for the constructor ~ |
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549 |
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550 Many languages use the class name for the constructor method. A disadvantage |
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551 is that quite often this is a long name. And when changing the class name all |
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552 constructor methods need to be renamed. Not a big deal, but still a |
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553 disadvantage. |
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554 |
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555 Other languages, such as TypeScript, use a specific name, such as |
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556 "constructor()". That seems better. However, using "new" or "new()" to |
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557 create a new object has no obvious relation with "constructor()". |
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558 |
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559 For |Vim9| script using the same method name for all constructors seemed like |
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560 the right choice, and by calling it new() the relation between the caller and |
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561 the method being called is obvious. |
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562 |
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563 |
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564 No overloading of the constructor ~ |
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565 |
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566 In Vim script, both legacy and |Vim9| script, there is no overloading of |
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567 functions. That means it is not possible to use the same function name with |
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568 different types of arguments. Therefore there also is only one new() |
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569 constructor. |
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570 |
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571 With |Vim9| script it would be possible to support overloading, since |
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572 arguments are typed. However, this gets complicated very quickly. Looking at |
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573 a new() call one has to inspect the types of the arguments to know which of |
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574 several new() methods is actually being called. And that can require |
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575 inspecting quite a bit of code. For example, if one of the arguments is the |
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576 return value of a method, you need to find that method to see what type it is |
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577 returning. |
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578 |
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579 Instead, every constructor has to have a different name, starting with "new". |
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580 That way multiple constructors with different arguments are possible, while it |
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581 is very easy to see which constructor is being used. And the type of |
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582 arguments can be properly checked. |
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583 |
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584 |
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585 No overloading of methods ~ |
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586 |
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587 Same reasoning as for the constructor: It is often not obvious what type |
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588 arguments have, which would make it difficult to figure out what method is |
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589 actually being called. Better just give the methods a different name, then |
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590 type checking will make sure it works as you intended. This rules out |
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591 polymorphism, which we don't really need anyway. |
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592 |
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593 |
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594 Using "this.member" everywhere ~ |
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595 |
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596 The object members in various programming languages can often be accessed in |
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597 different ways, depending on the location. Sometimes "this." has to be |
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598 prepended to avoid ambiguity. They are usually declared without "this.". |
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599 That is quite inconsistent and sometimes confusing. |
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600 |
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601 A very common issue is that in the constructor the arguments use the same name |
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602 as the object member. Then for these members "this." needs to be prefixed in |
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603 the body, while for other members this is not needed and often omitted. This |
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604 leads to a mix of members with and without "this.", which is inconsistent. |
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605 |
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606 For |Vim9| classes the "this." prefix is always used. Also for declaring the |
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607 members. Simple and consistent. When looking at the code inside a class it's |
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608 also directly clear which variable references are object members and which |
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609 aren't. |
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610 |
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611 |
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612 Single inheritance and interfaces ~ |
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613 |
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614 Some languages support multiple inheritance. Although that can be useful in |
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615 some cases, it makes the rules of how a class works quite complicated. |
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616 Instead, using interfaces to declare what is supported is much simpler. The |
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617 very popular Java language does it this way, and it should be good enough for |
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618 Vim. The "keep it simple" rule applies here. |
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619 |
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620 Explicitly declaring that a class supports an interface makes it easy to see |
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621 what a class is intended for. It also makes it possible to do proper type |
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622 checking. When an interface is changed any class that declares to implement |
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623 it will be checked if that change was also changed. The mechanism to assume a |
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624 class implements an interface just because the methods happen to match is |
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625 brittle and leads to obscure problems, let's not do that. |
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626 |
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627 |
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628 Using class members ~ |
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629 |
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630 Using "static member" to declare a class member is very common, nothing new |
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631 here. In |Vim9| script these can be accessed directly by their name. Very |
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632 much like how a script-local variable can be used in a function. Since object |
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633 members are always accessed with "this." prepended, it's also quickly clear |
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634 what kind of member it is. |
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635 |
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636 TypeScript prepends the class name before the class member, also inside the |
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637 class. This has two problems: The class name can be rather long, taking up |
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638 quite a bit of space, and when the class is renamed all these places need to |
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639 be changed too. |
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640 |
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641 |
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642 Using "ClassName.new()" to construct an object ~ |
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643 |
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644 Many languages use the "new" operator to create an object, which is actually |
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645 kind of strange, since the constructor is defined as a method with arguments, |
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646 not a command. TypeScript also has the "new" keyword, but the method is |
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647 called "constructor()", it is hard to see the relation between the two. |
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648 |
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649 In |Vim9| script the constructor method is called new(), and it is invoked as |
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650 new(), simple and straightforward. Other languages use "new ClassName()", |
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651 while there is no ClassName() method, it's a method by another name in the |
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652 class called ClassName. Quite confusing. |
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653 |
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654 |
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655 Default read access to object members ~ |
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656 |
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657 Some users will remark that the access rules for object members are |
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658 asymmetric. Well, that is intentional. Changing a value is a very different |
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659 action than reading a value. The read operation has no side effects, it can |
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660 be done any number of times without affecting the object. Changing the value |
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661 can have many side effects, and even have a ripple effect, affecting other |
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662 objects. |
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663 |
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664 When adding object members one usually doesn't think much about this, just get |
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665 the type right. And normally the values are set in the new() method. |
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666 Therefore defaulting to read access only "just works" in most cases. And when |
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667 directly writing you get an error, which makes you wonder if you actually want |
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668 to allow that. This helps writing code with fewer mistakes. |
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669 |
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670 |
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671 Making object members private with an underscore ~ |
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672 |
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673 When an object member is private, it can only be read and changed inside the |
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674 class (and in sub-classes), then it cannot be used outside of the class. |
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675 Prepending an underscore is a simple way to make that visible. Various |
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676 programming languages have this as a recommendation. |
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677 |
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678 In case you change your mind and want to make the object member accessible |
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679 outside of the class, you will have to remove the underscore everywhere. |
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680 Since the name only appears in the class (and sub-classes) they will be easy |
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681 to find and change. |
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682 |
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683 The other way around is much harder: you can easily prepend an underscore to |
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684 the object member inside the class to make it private, but any usage elsewhere |
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685 you will have to track down and change. You may have to make it a "set" |
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686 method call. This reflects the real world problem that taking away access |
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687 requires work to be done for all places where that access exists. |
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688 |
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689 An alternative would have been using the "private" keyword, just like "public" |
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690 changes the access in the other direction. Well, that's just to reduce the |
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691 number of keywords. |
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692 |
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693 |
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694 No protected object members ~ |
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695 |
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696 Some languages provide several ways to control access to object members. The |
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697 most known is "protected", and the meaning varies from language to language. |
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698 Others are "shared", "private" and even "friend". |
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699 |
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700 These rules make life more difficult. That can be justified in projects where |
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701 many people work on the same, complex code where it is easy to make mistakes. |
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702 Especially when refactoring or other changes to the class model. |
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703 |
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704 The Vim scripts are expected to be used in a plugin, with just one person or a |
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705 small team working on it. Complex rules then only make it more complicated, |
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706 the extra safety provide by the rules isn't really needed. Let's just keep it |
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707 simple and not specify access details. |
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708 |
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709 |
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710 ============================================================================== |
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711 |
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712 10. To be done later |
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713 |
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714 Can a newSomething() constructor invoke another constructor? If yes, what are |
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715 the restrictions? |
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716 |
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717 Thoughts: |
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718 - Generics for a class: `class <Tkey, Tentry>` |
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719 - Generics for a function: `def <Tkey> GetLast(key: Tkey)` |
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720 - Mixins: not sure if that is useful, leave out for simplicity. |
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721 |
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722 Some things that look like good additions: |
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723 - For testing: Mock mechanism |
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724 |
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725 An important class to be provided is "Promise". Since Vim is single |
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726 threaded, connecting asynchronous operations is a natural way of allowing |
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727 plugins to do their work without blocking the user. It's a uniform way to |
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728 invoke callbacks and handle timeouts and errors. |
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729 |
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730 |
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731 vim:tw=78:ts=8:noet:ft=help:norl: |