Golang方法调用值拷贝与引用拷贝

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<strong>1 方法调用采用值拷贝</strong> <br /> <strong>1.1 array</strong> <br /> golang中以array作为参数的方法调用,方法接收的是整个array的值拷贝,所以方法中对array的item重新赋值不起作用。 如以下代码所示,输出为[1, 2, 3]。 <div class="dp-highlighter"><div class="bar"></div><ol start="1" class="dp-j"><li class="alt"><span><span class="keyword">package</span><span>&nbsp;main&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">import</span><span>&nbsp;</span><span class="string">"fmt"</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span>func&nbsp;modify(a&nbsp;[<span class="number">3</span><span>]</span><span class="keyword">int</span><span>)&nbsp;{&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;a[<span class="number">0</span><span>]&nbsp;=&nbsp;</span><span class="number">4</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>}&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span>func&nbsp;main()&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;a&nbsp;:=&nbsp;[<span class="number">3</span><span>]</span><span class="keyword">int</span><span>{</span><span class="number">1</span><span>,&nbsp;</span><span class="number">2</span><span>,&nbsp;</span><span class="number">3</span><span>}&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;modify(a)&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(a)&nbsp;&nbsp;</span></li><li class="alt"><span>}&nbsp;&nbsp;</span></li></ol></div> <br /> <strong>1.2 struct</strong> <br /> 如下代码传参为struct值拷贝,modify方法或modify函数对person的name属性重新赋值不起作用。 <div class="dp-highlighter"><div class="bar"></div><ol start="1" class="dp-j"><li class="alt"><span><span class="keyword">package</span><span>&nbsp;main&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">import</span><span>&nbsp;</span><span class="string">"fmt"</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span>type&nbsp;person&nbsp;struct&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;name&nbsp;string&nbsp;&nbsp;</span></li><li class="alt"><span>}&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span>func&nbsp;(p&nbsp;person)&nbsp;modify()&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;p.name&nbsp;=&nbsp;<span class="string">"jacky"</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>}&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span>func&nbsp;modify(p&nbsp;person)&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;p.name&nbsp;=&nbsp;<span class="string">"jacky"</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>}&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span>func&nbsp;main()&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;p&nbsp;:=&nbsp;person{<span class="string">"larry"</span><span>}&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;p.modify()&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="comment">//&nbsp;modify(p)</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(p)&nbsp;&nbsp;</span></li><li class=""><span>}&nbsp;&nbsp;</span></li></ol></div> <br /> <strong>2 方法调用采用引用拷贝</strong> <br /> <strong>2.1 slice</strong> <br /> slice作为底层的数组引用,方法调用采用的是引用的拷贝。 所以,如下第一段代码,函数的引用拷贝与原始引用指向同一块数组,对slice的item重新赋值是生效的,输出为[4, 2, 3]。 <div class="dp-highlighter"><div class="bar"></div><ol start="1" class="dp-j"><li class="alt"><span><span class="keyword">package</span><span>&nbsp;main&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">import</span><span>&nbsp;</span><span class="string">"fmt"</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span>func&nbsp;modify(s&nbsp;[]<span class="keyword">int</span><span>)&nbsp;{&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;s[<span class="number">0</span><span>]&nbsp;=&nbsp;</span><span class="number">4</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>}&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span>func&nbsp;main()&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;s&nbsp;:=&nbsp;[]<span class="keyword">int</span><span>{</span><span class="number">1</span><span>,&nbsp;</span><span class="number">2</span><span>,&nbsp;</span><span class="number">3</span><span>}&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;modify(s)&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(s)&nbsp;&nbsp;</span></li><li class="alt"><span>}&nbsp;&nbsp;</span></li></ol></div> 但第二段代码,输出结果未变化,仍为[1, 2, 3]。是因为对引用的拷贝重新赋值,并不会更改原始引用。 <div class="dp-highlighter"><div class="bar"></div><ol start="1" class="dp-j"><li class="alt"><span><span class="keyword">package</span><span>&nbsp;main&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">import</span><span>&nbsp;</span><span class="string">"fmt"</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span>func&nbsp;modify(s&nbsp;[]<span class="keyword">int</span><span>)&nbsp;{&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;s&nbsp;=&nbsp;append(s,&nbsp;<span class="number">4</span><span>)&nbsp;&nbsp;</span></span></li><li class="alt"><span>}&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span>func&nbsp;main()&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;s&nbsp;:=&nbsp;[]<span class="keyword">int</span><span>{</span><span class="number">1</span><span>,&nbsp;</span><span class="number">2</span><span>,&nbsp;</span><span class="number">3</span><span>}&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;modify(s)&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(s)&nbsp;&nbsp;</span></li><li class="alt"><span>}&nbsp;&nbsp;</span></li></ol></div> 所以对slice进行append操作,需要将其作为返回值返回,如以下代码所示,输出为[1 2 3 4]。 <div class="dp-highlighter"><div class="bar"></div><ol start="1" class="dp-j"><li class="alt"><span><span class="keyword">package</span><span>&nbsp;main&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">import</span><span>&nbsp;</span><span class="string">"fmt"</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span>func&nbsp;modify(s&nbsp;[]<span class="keyword">int</span><span>)&nbsp;[]</span><span class="keyword">int</span><span>&nbsp;{&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;s&nbsp;=&nbsp;append(s,&nbsp;<span class="number">4</span><span>)&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">return</span><span>&nbsp;s&nbsp;&nbsp;</span></span></li><li class=""><span>}&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;</span></li><li class=""><span>func&nbsp;main()&nbsp;{&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;s&nbsp;:=&nbsp;[]<span class="keyword">int</span><span>{</span><span class="number">1</span><span>,&nbsp;</span><span class="number">2</span><span>,&nbsp;</span><span class="number">3</span><span>}&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;s&nbsp;=&nbsp;modify(s)&nbsp;&nbsp;</span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(s)&nbsp;&nbsp;</span></li><li class=""><span>}&nbsp;&nbsp;</span></li></ol></div> <br /> <strong>2.2 struct pointer</strong> <br /> 若想改变struct的属性值,传参采用struct pointer。 <div class="dp-highlighter"><div class="bar"></div><ol start="1" class="dp-j"><li class="alt"><span><span class="keyword">package</span><span>&nbsp;main&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span><span class="keyword">import</span><span>&nbsp;</span><span class="string">"fmt"</span><span>&nbsp;&nbsp;</span></span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span>type&nbsp;person&nbsp;struct&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;name&nbsp;string&nbsp;&nbsp;</span></li><li class="alt"><span>}&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span>func&nbsp;(p&nbsp;*person)&nbsp;modify()&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;p.name&nbsp;=&nbsp;<span class="string">"jacky"</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>}&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span>func&nbsp;modify(p&nbsp;*person)&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;p.name&nbsp;=&nbsp;<span class="string">"jacky"</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>}&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;</span></li><li class="alt"><span>func&nbsp;main()&nbsp;{&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;p&nbsp;:=&nbsp;&amp;person{<span class="string">"larry"</span><span>}&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;p.modify()&nbsp;&nbsp;</span></li><li class=""><span>&nbsp;&nbsp;&nbsp;&nbsp;<span class="comment">//&nbsp;modify(p)</span><span>&nbsp;&nbsp;</span></span></li><li class="alt"><span>&nbsp;&nbsp;&nbsp;&nbsp;fmt.Println(p)&nbsp;&nbsp;</span></li><li class=""><span>}&nbsp;&nbsp;</span></li></ol></div> <br /> 原文地址:https://leileiluoluo.com/posts/golang-method-calling-value-copy-or-reference-copy.html

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