golang 对接口方法使用*还是实例的坑
发布时间：2022-01-19 编辑：jiaochengji.com
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<svg xmlns="http://www.w3.org/2000/svg" style="display: none;"><path stroke-linecap="round" d="M5,0 0,2.5 5,5z" id="raphael-marker-block" style="-webkit-tap-highlight-color: rgba(0, 0, 0, 0);"/></svg><h2>对go来说，如果一个接口定义了</h2>
<pre class=" language-go"><code class="prism language-go"><span class="token keyword">type</span> I <span class="token keyword">interface</span><span class="token punctuation">{</span>
<span class="token function">F</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span>
</code></pre>
<h2>则对一个Object，以下两种皆符合实现了接口</h2>
<pre class=" language-go"><code class="prism language-go"><span class="token keyword">type</span> Object Type<span class="token punctuation">{</span>
<span class="token punctuation">}</span>
<span class="token keyword">func</span> <span class="token punctuation">(</span>o <span class="token operator">*</span>Object<span class="token punctuation">)</span> <span class="token function">F</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token punctuation">}</span>
<span class="token comment">// 或者</span>
<span class="token keyword">func</span> <span class="token punctuation">(</span>o Object<span class="token punctuation">)</span><span class="token function">F</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span><span class="token punctuation">}</span>
</code></pre>
<h2>但是在使用时，如果涉及到interface装箱，就需要为对象指明取地址还是实例，比如:</h2>
<pre class=" language-go"><code class="prism language-go"><span class="token keyword">type</span> U <span class="token keyword">struct</span><span class="token punctuation">{</span>
<span class="token punctuation">}</span>
<span class="token keyword">func</span> <span class="token punctuation">(</span>u <span class="token operator">*</span>U<span class="token punctuation">)</span> <span class="token function">String</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token builtin">string</span><span class="token punctuation">{</span>
<span class="token keyword">return</span> <span class="token string">"ptr"</span>
<span class="token punctuation">}</span>
<span class="token keyword">func</span> <span class="token function">ToString</span><span class="token punctuation">(</span>arg <span class="token keyword">interface</span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token builtin">string</span><span class="token punctuation">{</span>
<span class="token keyword">switch</span> v<span class="token operator">:=</span>arg<span class="token punctuation">.</span><span class="token punctuation">(</span><span class="token keyword">type</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token keyword">case</span> fmt<span class="token punctuation">.</span>Stringer<span class="token punctuation">:</span>
<span class="token keyword">return</span> v<span class="token punctuation">.</span><span class="token function">String</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token keyword">default</span><span class="token punctuation">:</span>
<span class="token keyword">return</span> <span class="token string">""</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token keyword">func</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
u <span class="token operator">:=</span> U<span class="token punctuation">{</span><span class="token punctuation">}</span>
<span class="token comment">//则需要</span>
fmt<span class="token punctuation">.</span><span class="token function">Println</span><span class="token punctuation">(</span><span class="token function">ToString</span><span class="token punctuation">(</span><span class="token operator">&</span>u<span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span>
</code></pre>
如果改为：
<pre class=" language-go"><code class="prism language-go"><span class="token keyword">type</span> U <span class="token keyword">struct</span><span class="token punctuation">{</span> <span class="token punctuation">}</span> <span class="token keyword">func</span> <span class="token punctuation">(</span>u U<span class="token punctuation">)</span> <span class="token function">String</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token builtin">string</span><span class="token punctuation">{</span> <span class="token keyword">return</span> <span class="token string">"ptr"</span> <span class="token punctuation">}</span> <span class="token keyword">func</span> <span class="token function">ToString</span><span class="token punctuation">(</span>arg <span class="token keyword">interface</span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token builtin">string</span><span class="token punctuation">{</span> <span class="token keyword">switch</span> v<span class="token operator">:=</span>arg<span class="token punctuation">.</span><span class="token punctuation">(</span><span class="token keyword">type</span><span class="token punctuation">)</span><span class="token punctuation">{</span> <span class="token keyword">case</span> fmt<span class="token punctuation">.</span>Stringer<span class="token punctuation">:</span> <span class="token keyword">return</span> v<span class="token punctuation">.</span><span class="token function">String</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">default</span><span class="token punctuation">:</span> <span class="token keyword">return</span> <span class="token string">""</span> <span class="token punctuation">}</span> <span class="token punctuation">}</span> <span class="token keyword">func</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span> u <span class="token operator">:=</span> U<span class="token punctuation">{</span><span class="token punctuation">}</span> <span class="token comment">//则需要</span> fmt<span class="token punctuation">.</span><span class="token function">Println</span><span class="token punctuation">(</span><span class="token function">ToString</span><span class="token punctuation">(</span>u<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">}</span> </code></pre>二者的区别就在receiver一个是*U一个是U，对应的ToString(&u)和ToString(u)
这个坑要记住了
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