<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<title>Returning References</title>
</head>
<body><div class="manualnavbar" style="text-align: center;">
<div class="prev" style="text-align: left; float: left;"><a href="language.references.pass.html">Passing by Reference</a></div>
<div class="next" style="text-align: right; float: right;"><a href="language.references.unset.html">Unsetting References</a></div>
<div class="up"><a href="language.references.html">References Explained</a></div>
<div class="home"><a href="index.html">PHP Manual</a></div>
</div><hr /><div id="language.references.return" class="sect1">
<h2 class="title">Returning References</h2>
<p class="para">
Returning by reference is useful when you want to use a function
to find to which variable a reference should be bound. Do
<em class="emphasis">not</em> use return-by-reference to increase performance.
The engine will automatically optimize this on its own. Only return
references when you have a valid technical reason to do so. To
return references, use this syntax:
<div class="informalexample">
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">class </span><span style="color: #0000BB">foo </span><span style="color: #007700">{<br /> public </span><span style="color: #0000BB">$value </span><span style="color: #007700">= </span><span style="color: #0000BB">42</span><span style="color: #007700">;<br /><br /> public function &</span><span style="color: #0000BB">getValue</span><span style="color: #007700">() {<br /> return </span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">value</span><span style="color: #007700">;<br /> }<br />}<br /><br /></span><span style="color: #0000BB">$obj </span><span style="color: #007700">= new </span><span style="color: #0000BB">foo</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$myValue </span><span style="color: #007700">= &</span><span style="color: #0000BB">$obj</span><span style="color: #007700">-></span><span style="color: #0000BB">getValue</span><span style="color: #007700">(); </span><span style="color: #FF8000">// $myValue is a reference to $obj->value, which is 42.<br /></span><span style="color: #0000BB">$obj</span><span style="color: #007700">-></span><span style="color: #0000BB">value </span><span style="color: #007700">= </span><span style="color: #0000BB">2</span><span style="color: #007700">;<br />echo </span><span style="color: #0000BB">$myValue</span><span style="color: #007700">; </span><span style="color: #FF8000">// prints the new value of $obj->value, i.e. 2.<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
In this example, the property of the object returned by the
<var class="varname"><var class="varname">getValue</var></var> function would be set, not the
copy, as it would be without using reference syntax.
</p>
<blockquote class="note"><p><strong class="note">Note</strong>:
<span class="simpara">
Unlike parameter passing, here you have to use
<em>&</em> in both places - to indicate that you
want to return by reference, not a copy, and to indicate that
reference binding, rather than usual assignment, should be done
for <var class="varname"><var class="varname">$myValue</var></var>.
</span>
</p></blockquote>
<blockquote class="note"><p><strong class="note">Note</strong>:
<span class="simpara">
If you try to return a reference from a function with the syntax:
<em>return ($this->value);</em> this will <em class="emphasis">not</em>
work as you are attempting to return the result of an
<em class="emphasis">expression</em>, and not a variable, by reference. You can
only return variables by reference from a function - nothing else.
Since PHP 4.4.0 in the PHP 4 branch, and PHP 5.1.0 in the PHP 5 branch, an
<strong><code>E_NOTICE</code></strong> error is issued if the code tries to return
a dynamic expression or a result of the <em>new</em> operator.
</span>
</p></blockquote>
<p class="para">
To use the returned reference, you must use reference assigment:
<div class="informalexample">
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function &</span><span style="color: #0000BB">collector</span><span style="color: #007700">() {<br /> static </span><span style="color: #0000BB">$collection </span><span style="color: #007700">= array();<br /> return </span><span style="color: #0000BB">$collection</span><span style="color: #007700">;<br />}<br /></span><span style="color: #0000BB">$collection </span><span style="color: #007700">= &</span><span style="color: #0000BB">collector</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">$collection</span><span style="color: #007700">[] = </span><span style="color: #DD0000">'foo'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
To pass the returned reference to another function expecting a reference
you can use this syntax:
<div class="informalexample">
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function &</span><span style="color: #0000BB">collector</span><span style="color: #007700">() {<br /> static </span><span style="color: #0000BB">$collection </span><span style="color: #007700">= array();<br /> return </span><span style="color: #0000BB">$collection</span><span style="color: #007700">;<br />}<br /></span><span style="color: #0000BB">array_push</span><span style="color: #007700">(</span><span style="color: #0000BB">collector</span><span style="color: #007700">(), </span><span style="color: #DD0000">'foo'</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<blockquote class="note"><p><strong class="note">Note</strong>:
<span class="simpara">
Note that <em>array_push(&collector(), 'foo');</em> will
<em class="emphasis">not</em> work, it results in a fatal error.
</span>
</p></blockquote>
</div><hr /><div class="manualnavbar" style="text-align: center;">
<div class="prev" style="text-align: left; float: left;"><a href="language.references.pass.html">Passing by Reference</a></div>
<div class="next" style="text-align: right; float: right;"><a href="language.references.unset.html">Unsetting References</a></div>
<div class="up"><a href="language.references.html">References Explained</a></div>
<div class="home"><a href="index.html">PHP Manual</a></div>
</div></body></html>
