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<span class=screen-reader-text>Posted on</span>
<time class=entry-date datetime=2012-04-03T00:00:00Z>2012, Apr 03</time></span>
<span class=reading-time>
One min read</span></div></div></header><div class="container entry-content custom"><p>C++ allows to declare one class as a friend of another one.</p><p>This can be useful if you want to keep some details of class protected, but available for another particular (friend) class.</p><p>For example this can be used in <a href=http://sourcemaking.com/design_patterns/state>State pattern</a> to keep
setState method of context class protected.</p><p>To emulate this in PHP we can inherit state class from context class:</p><div class=highlight><pre tabindex=0 style=color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-php data-lang=php><span style=display:flex>
<span style=color:#66d9ef>class <span style=color:#a6e22e>AContext</span> {
</span></span><span style=display:flex>
<span style=color:#66d9ef>private $_state;
</span></span><span style=display:flex>
</span><span style=display:flex>
<span style=color:#66d9ef>protected <span style=color:#66d9ef>function</span> <span style=color:#a6e22e>setState</span>(<span style=color:#a6e22e>AState</span> $state) {
</span></span><span style=display:flex>
$this<span style=color:#f92672>-><span style=color:#a6e22e>_state</span> <span style=color:#f92672>=</span> $state;
</span></span><span style=display:flex>
}
</span><span style=display:flex>
</span><span style=display:flex>
<span style=color:#66d9ef>public <span style=color:#66d9ef>function</span> <span style=color:#a6e22e>request</span>() {
</span></span><span style=display:flex>
$this<span style=color:#f92672>-><span style=color:#a6e22e>_state</span><span style=color:#f92672>-></span><span style=color:#a6e22e>handle</span>();
</span></span><span style=display:flex>
}
</span><span style=display:flex>
</span><span style=display:flex>
}
</span><span style=display:flex>
</span><span style=display:flex>
<span style=color:#66d9ef>abstract <span style=color:#66d9ef>class</span> <span style=color:#a6e22e>AState</span> <span style=color:#66d9ef>extends</span> <span style=color:#a6e22e>AContext</span> {
</span></span><span style=display:flex>
<span style=color:#66d9ef>private $_owner;
</span></span><span style=display:flex>
</span><span style=display:flex>
<span style=color:#66d9ef>public <span style=color:#66d9ef>function</span> __construct(<span style=color:#a6e22e>AContext</span> $owner) {
</span></span><span style=display:flex>
$this<span style=color:#f92672>-><span style=color:#a6e22e>_owner</span> <span style=color:#f92672>=</span> $owner;
</span></span><span style=display:flex>
}
</span><span style=display:flex>
</span><span style=display:flex>
<span style=color:#66d9ef>protected <span style=color:#66d9ef>function</span> <span style=color:#a6e22e>getOwner</span>() {
</span></span><span style=display:flex>
<span style=color:#66d9ef>return $this<span style=color:#f92672>-></span><span style=color:#a6e22e>_owner</span>;
</span></span><span style=display:flex>
}
</span><span style=display:flex>
</span><span style=display:flex>
<span style=color:#66d9ef>abstract <span style=color:#66d9ef>function</span> <span style=color:#a6e22e>handle</span>();
</span></span><span style=display:flex>
</span><span style=display:flex>
}
</span><span style=display:flex>
</span><span style=display:flex>
<span style=color:#66d9ef>class <span style=color:#a6e22e>AConcreteState</span> <span style=color:#66d9ef>extends</span> <span style=color:#a6e22e>AState</span> {
</span></span><span style=display:flex>
</span><span style=display:flex>
<span style=color:#66d9ef>public <span style=color:#66d9ef>function</span> <span style=color:#a6e22e>handle</span>() {
</span></span><span style=display:flex>
<span style=color:#f92672>…
</span></span><span style=display:flex>
$this<span style=color:#f92672>-><span style=color:#a6e22e>getOwner</span>()<span style=color:#f92672>-></span><span style=color:#a6e22e>setState</span>(<span style=color:#66d9ef>new</span> <span style=color:#a6e22e>AnotherState</span>($this<span style=color:#f92672>-></span><span style=color:#a6e22e>getOwner</span>());
</span></span><span style=display:flex>
}
</span><span style=display:flex>
}
</span><span style=display:flex>
</span><span style=display:flex>
<span style=color:#66d9ef>class <span style=color:#a6e22e>AnotherState</span> <span style=color:#66d9ef>extends</span> <span style=color:#a6e22e>AState</span> {
</span></span><span style=display:flex>
<span style=color:#f92672>…
</span></span><span style=display:flex>
}
</span></code></pre></div><a href=https://stackexchange.com/users/261528>
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