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<title>Reference: assign – De Re @property</title>
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<h1>Reference: assign</h1>
<div>
<table>
<tbody>
<tr>
<td>Types</td>
<td>all</td>
</tr>
<tr>
<td>Signature Letter</td>
<td>none</td>
</tr>
<tr>
<td>Portability</td>
<td>all</td>
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<div class="language-objc highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">@property</span><span class="p">(</span><span class="n">assign</span><span class="p">)</span> <span class="n">id</span> <span class="n">propertyName</span><span class="p">;</span>
</code></pre></div></div>
<p>The <code class="language-plaintext highlighter-rouge">assign</code> attribute is the default attribute for all attributes,
and is therefore often omitted on non-object properties. For object
properties that are actually <code class="language-plaintext highlighter-rouge">assign</code>, it’s very bad style to omit it.</p>
<p>The <code class="language-plaintext highlighter-rouge">assign</code> attribute is used with <code class="language-plaintext highlighter-rouge">@property</code> declarations in Objective-C for
object properties that should not retain ownership of the assigned value. This
is commonly used for delegates or references to owner objects to avoid retain
cycles.</p>
<ul>
<li>Simply assigns the pointer without increasing the retain count</li>
<li>Does not release the old value before assigning the new one</li>
<li>Does not ensure the property maintains ownership of its assigned object</li>
<li>Useful for avoiding retain cycles in parent-child or delegate relationships</li>
</ul>
<h3 id="caveat">Caveat</h3>
<ul>
<li>Can lead to dangling pointers, if the assigned object is prematurely deallocated</li>
</ul>
<h3 id="example">Example</h3>
<div class="language-objc highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">@interface</span> <span class="nc">ChildViewController</span> <span class="p">:</span> <span class="nc">UIViewController</span>
<span class="k">@property</span><span class="p">(</span> <span class="n">assign</span><span class="p">)</span> <span class="n">UIViewController</span> <span class="o">*</span><span class="n">parentViewController</span><span class="p">;</span>
<span class="k">@end</span>
<span class="k">@implementation</span> <span class="nc">ChildViewController</span>
<span class="k">-</span> <span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="nf">setParentController</span><span class="p">:(</span><span class="n">UIViewController</span> <span class="o">*</span><span class="p">)</span> <span class="n">controller</span>
<span class="p">{</span>
<span class="p">[</span><span class="n">self</span> <span class="nf">setParentViewController</span><span class="p">:</span><span class="n">controller</span><span class="p">];</span>
<span class="p">}</span>
<span class="k">@end</span>
</code></pre></div></div>
<h3 id="assign-accessors">assign accessors</h3>
<p>These are the equivalent accessor implementation for an <code class="language-plaintext highlighter-rouge">assign</code> object property:</p>
<div class="language-objc highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">-</span> <span class="p">(</span><span class="n">id</span><span class="p">)</span> <span class="n">object</span>
<span class="p">{</span>
<span class="k">return</span><span class="p">(</span> <span class="n">_object</span><span class="p">);</span>
<span class="p">}</span>
<span class="k">-</span> <span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="nf">setObject</span><span class="p">:(</span><span class="n">id</span><span class="p">)</span> <span class="n">object</span>
<span class="p">{</span>
<span class="n">_object</span> <span class="o">=</span> <span class="n">object</span><span class="p">;</span>
<span class="p">}</span>
</code></pre></div></div>
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