ios - 在 init 中返回 nil 会导致内存泄漏吗？
<p><p><code>init</code>中ARC下返回<code>nil</code>会导致内存泄漏，当<code></code>已经被调用，然后返回nil？这是合法的用法吗？</p>
<pre><code>- (id)init {
self = ;
if (self) {
...
return nil;
...
}
return self;
}
</code></pre></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><p>首先:对于引用 ARC 的 Q 从未阅读过 Apple 的文档，而是 clang 的。 </p>
<p>Apple 的文档只是隐藏(隐藏？)<code>-init</code> 的执行，并且有这样的错误示例:</p>
<pre><code>id ref = [ init]
</code></pre>
<p>你会发现像“<code>+alloc</code> 转移所有权”这样的语句。这至少具有误导性，因为 <code>-init</code> 的返回值而不是 <em></em> <code>+alloc</code> 的返回值被存储。 </p>
<p>到目前为止，clang 的文档更好、更精确。基本上他们说，<code>+alloc</code> 是所有权转移<em>和</em> <code>-init</code> 是所有权消耗和所有权转移。 </p>
<p> <a href="http://clang.llvm.org/docs/AutomaticReferenceCounting.html#semantics-of-init" rel="noreferrer noopener nofollow">http://clang.llvm.org/docs/AutomaticReferenceCounting.html#semantics-of-init</a> </p>
<blockquote>
<p>Methods in the init family implicitly consume their self parameter and return a retained object. </p>
</blockquote>
<p>那么让我们看一下通常的代码:</p>
<pre><code>id ref = ;
// ref is strong: RC is +1;
id ref = ;
// Three things happen her:
// 1. -init is executed
// 2. The new value is stored
// 3. The old value of ref is lost
// 1. -init is executed
// self is (silently) passed to the receiver
- (id)init
{
// Since self is strong (+1), RC is +2 now
// Since -init is ownership consuming (-1), RC is +1 now
…
return self;
// Since -init is ownership transferring (+1), RC is +2 now
}
// 2. The new value is stored
// The value comes from an ownership transfer method, so the assignment to strong ref is neutral (0), RC is still +2
// 3. The old value is lost (-1), RC is +1
</code></pre>
<p>结果是该对象的 RC 为 +1，并且您在该代码区域中有一个对它的强引用。一切都很好。 (当然有很大的优化潜力，因为在大多数情况下 <code>self</code> 和 <code>ref</code> 都没有改变，但让我们保持正常的轨道。)</p>
<p>让我们在 <code>-init</code> 中更改 <code>self</code>:</p>
<pre><code>id ref = ; // Ownership transfer. RC is +1;
id ref = ;
// Three things happen her:
// 1. -init is executed
// 2. The new value is stored
// 3. The old value of ref is lost
// 1. -init is executed
// self is (silently) passed to the receiver
- (id)init
{
// Since self is strong (+1), RC is +2 now
// Since -init is ownership consuming (-1), RC is +1 now
// Let's return nil as in your example
return nil;
// Because nil is returned, virtually the RC of nil is increased. self's RC == +1 is unchanged.
}
// 2. The new value is stored
// The new value is nil.
// However the value comes from an ownership transfer method, so the assignment to strong ref is neutral (0), RC is still +1
// 3. The old value is lost (your old ref and the self while executing -init) (-1), RC is 0
// The old object is dealloced, if you do not have another ref to it. Nothing leaks.
</code></pre></p>
<p style="font-size: 20px;">关于ios - 在 init 中返回 nil 会导致内存泄漏吗？，我们在Stack Overflow上找到一个类似的问题：
<a href="https://stackoverflow.com/questions/29603467/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/29603467/
</a>
</p>
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