golang 切片copy复制和等号复制的区别

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结论：copy复制会比等号复制慢。但是copy复制为值复制，改变原切片的值不会影响新切片。而等号复制为指针复制，改变原切片或新切片都会对另一个产生影响。

测试复制速度：

<pre><code class="lang-go hljs"><span class="token keyword">func</span> <span class="token function">TestArr1</span><span class="token punctuation">(</span>t <span class="token operator">*</span>testing<span class="token punctuation">.</span>T<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">var</span> a <span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token builtin">int</span> <span class="token keyword">for</span> i <span class="token operator">:=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator"><</span> <span class="token number">100000000</span><span class="token punctuation">;</span> i<span class="token operator"> </span> <span class="token punctuation">{</span> a <span class="token operator">=</span> <span class="token function">append</span><span class="token punctuation">(</span>a<span class="token punctuation">,</span> i<span class="token punctuation">)</span> <span class="token punctuation">}</span> start <span class="token operator">:=</span> time<span class="token punctuation">.</span><span class="token function">Now</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">UnixNano</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">var</span> b <span class="token operator">=</span> <span class="token function">make</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token builtin">int</span><span class="token punctuation">,</span> <span class="token number">1000000</span><span class="token punctuation">)</span> <span class="token function">copy</span><span class="token punctuation">(</span>b<span class="token punctuation">,</span> a<span class="token punctuation">)</span> end <span class="token operator">:=</span> time<span class="token punctuation">.</span><span class="token function">Now</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">UnixNano</span><span class="token punctuation">(</span><span class="token punctuation">)</span> fmt<span class="token punctuation">.</span><span class="token function">Println</span><span class="token punctuation">(</span>end <span class="token operator">-</span> start<span class="token punctuation">)</span> <span class="token punctuation">}</span> </code></pre>

结果为 5001100

<pre><code class="lang-go hljs"><span class="token keyword">func</span> <span class="token function">TestArr2</span><span class="token punctuation">(</span>t <span class="token operator">*</span>testing<span class="token punctuation">.</span>T<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">var</span> a <span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token builtin">int</span> <span class="token keyword">for</span> i <span class="token operator">:=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator"><</span> <span class="token number">100000000</span><span class="token punctuation">;</span> i<span class="token operator"> </span> <span class="token punctuation">{</span> a <span class="token operator">=</span> <span class="token function">append</span><span class="token punctuation">(</span>a<span class="token punctuation">,</span> i<span class="token punctuation">)</span> <span class="token punctuation">}</span> start <span class="token operator">:=</span> time<span class="token punctuation">.</span><span class="token function">Now</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">UnixNano</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">var</span> b <span class="token operator">=</span> a<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">:</span><span class="token number">1000000</span><span class="token punctuation">]</span> end <span class="token operator">:=</span> time<span class="token punctuation">.</span><span class="token function">Now</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">UnixNano</span><span class="token punctuation">(</span><span class="token punctuation">)</span> fmt<span class="token punctuation">.</span><span class="token function">Println</span><span class="token punctuation">(</span>end <span class="token operator">-</span> start<span class="token punctuation">)</span> <span class="token boolean">_</span> <span class="token operator">=</span> b <span class="token punctuation">}</span> </code></pre>

结果为0
结论：等号复制要比copy赋值速度快

测试更改原切片是否影响新切片：

<pre><code class="lang-go hljs"><span class="token keyword">func</span> <span class="token function">TestArr1</span><span class="token punctuation">(</span>t <span class="token operator">*</span>testing<span class="token punctuation">.</span>T<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">var</span> a <span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token builtin">int</span> <span class="token keyword">for</span> i <span class="token operator">:=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator"><</span> <span class="token number">100</span><span class="token punctuation">;</span> i<span class="token operator"> </span> <span class="token punctuation">{</span> a <span class="token operator">=</span> <span class="token function">append</span><span class="token punctuation">(</span>a<span class="token punctuation">,</span> i<span class="token punctuation">)</span> <span class="token punctuation">}</span> <span class="token keyword">var</span> b <span class="token operator">=</span> <span class="token function">make</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token builtin">int</span><span class="token punctuation">,</span> <span class="token number">10</span><span class="token punctuation">)</span> <span class="token function">copy</span><span class="token punctuation">(</span>b<span class="token punctuation">,</span> a<span class="token punctuation">)</span> a<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token number">999</span> fmt<span class="token punctuation">.</span><span class="token function">Println</span><span class="token punctuation">(</span>b<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token punctuation">}</span> </code></pre>

结果0

<pre><code class="lang-go hljs"><span class="token keyword">func</span> <span class="token function">TestArr2</span><span class="token punctuation">(</span>t <span class="token operator">*</span>testing<span class="token punctuation">.</span>T<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">var</span> a <span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token builtin">int</span> <span class="token keyword">for</span> i <span class="token operator">:=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator"><</span> <span class="token number">100</span><span class="token punctuation">;</span> i<span class="token operator"> </span> <span class="token punctuation">{</span> a <span class="token operator">=</span> <span class="token function">append</span><span class="token punctuation">(</span>a<span class="token punctuation">,</span> i<span class="token punctuation">)</span> <span class="token punctuation">}</span> <span class="token keyword">var</span> b <span class="token operator">=</span> a<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">:</span><span class="token number">10</span><span class="token punctuation">]</span> a<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token number">999</span> fmt<span class="token punctuation">.</span><span class="token function">Println</span><span class="token punctuation">(</span>b<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token punctuation">}</span> </code></pre>

结果 999
结论：copy为值复制，更改原切片不会影响新切片，而等号复制相反

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