Lua 面向对象

topic
5.5k 词

隐藏 self 参数

用 lua 进行面向对象的编程

  • 声明方法和调用方法统一用 ":"
  • 属性的定义和调用全部用 "."

定义的时候冒号默认接收 self 参数，调用的时候默认传递调用者自身作为参数，而点号要显式传递或接收 self 参数。

一个简单的类

function class(classname, super)
	local superType = type(super)
	local cls

<span class="k">if</span> <span class="n">superType</span> <span class="o">~=</span> <span class="s2">&#34;function&#34;</span> <span class="ow">and</span> <span class="n">superType</span> <span class="o">~=</span> <span class="s2">&#34;table&#34;</span> <span class="k">then</span>
	<span class="n">superType</span> <span class="o">=</span> <span class="kc">nil</span>
	<span class="n">super</span> <span class="o">=</span> <span class="kc">nil</span>
<span class="k">end</span>

<span class="c1">-- inherited(继承) from Lua Object</span>
<span class="k">if</span> <span class="n">super</span> <span class="k">then</span> <span class="c1">-- 复制基类方法</span>
	<span class="n">cls</span> <span class="o">=</span> <span class="p">{}</span>
	<span class="nb">setmetatable</span><span class="p">(</span><span class="n">cls</span><span class="p">,</span> <span class="p">{</span><span class="n">__index</span> <span class="o">=</span> <span class="n">super</span><span class="p">})</span>
	<span class="n">cls</span><span class="p">.</span><span class="n">super</span> <span class="o">=</span> <span class="n">super</span>
<span class="k">else</span>
	<span class="n">cls</span> <span class="o">=</span> <span class="p">{</span><span class="n">ctor</span> <span class="o">=</span> <span class="k">function</span><span class="p">()</span> <span class="k">end</span><span class="p">}</span> <span class="c1">-- 构造函数</span>
<span class="k">end</span>

<span class="n">cls</span><span class="p">.</span><span class="n">__cname</span> <span class="o">=</span> <span class="n">classname</span>
<span class="n">cls</span><span class="p">.</span><span class="n">__index</span> <span class="o">=</span> <span class="n">cls</span>

<span class="k">function</span> <span class="nc">cls</span><span class="p">.</span><span class="nf">new</span><span class="p">(</span><span class="o">...</span><span class="p">)</span> <span class="c1">-- 实例化</span>
	<span class="kd">local</span> <span class="n">obj_data</span> <span class="o">=</span> <span class="p">{}</span>
	<span class="kd">local</span> <span class="n">cls_name</span> <span class="o">=</span> <span class="n">cls</span><span class="p">.</span><span class="n">__cname</span>
	
	<span class="kd">local</span> <span class="n">instance</span> <span class="o">=</span> <span class="nb">setmetatable</span><span class="p">(</span><span class="n">obj_data</span><span class="p">,</span> <span class="n">cls</span><span class="p">)</span>
	<span class="n">instance</span><span class="p">.</span><span class="n">class</span> <span class="o">=</span> <span class="n">cls</span>
	<span class="n">instance</span><span class="p">:</span><span class="n">ctor</span><span class="p">(</span><span class="o">...</span><span class="p">)</span>
	<span class="k">return</span> <span class="n">instance</span>
<span class="k">end</span>
<span class="k">return</span> <span class="n">cls</span>



end

在 lua 中不存在类的定义这样的概念，不管是类的定义还是类的实例都是通过 lua table 来模拟的。实现的 lua 面向对象是 prototype（原型）方式的，即类是一个 lua table，这个 table 定义了类的原型，而类的实例是基于这个原型的另一个 lua table。

实现 lua 面向对象可以分解为类的定义和类的实例化两部分。类的定义主要实现继承，让子类拥有父类的方法集；类的实例化需要解决实例对象如何共享类的方法集，但独享自己的成员变量实例。

子类在定义时复制所有基类的方法，在实例化时将该类作为 metatable 的 __index 赋值给实例。

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