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</div><hr /><div id="language.operators.assignment" class="sect1">
<h2 class="title">Assignment Operators</h2>
<p class="simpara">
The basic assignment operator is "=". Your first inclination might
be to think of this as "equal to". Don't. It really means that the
left operand gets set to the value of the expression on the
right (that is, "gets set to").
</p>
<p class="para">
The value of an assignment expression is the value assigned. That
is, the value of "<em>$a = 3</em>" is 3. This allows you to do some tricky
things:
<div class="informalexample">
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /><br />$a </span><span style="color: #007700">= (</span><span style="color: #0000BB">$b </span><span style="color: #007700">= </span><span style="color: #0000BB">4</span><span style="color: #007700">) + </span><span style="color: #0000BB">5</span><span style="color: #007700">; </span><span style="color: #FF8000">// $a is equal to 9 now, and $b has been set to 4.<br /><br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">
For <span class="type"><span class="type arrays">arrays</span></span>, assigning a value to a named key is performed using
the "=>" operator. The <a href="language.operators.precedence.html" class="link">precedence</a>
of this operator is the same as other assignment operators.
</p>
<p class="para">
In addition to the basic assignment operator, there are "combined
operators" for all of the <a href="language.operators.html" class="link">binary
arithmetic</a>, array union and string operators that allow you to use a value in an
expression and then set its value to the result of that expression. For
example:
<div class="informalexample">
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /><br />$a </span><span style="color: #007700">= </span><span style="color: #0000BB">3</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$a </span><span style="color: #007700">+= </span><span style="color: #0000BB">5</span><span style="color: #007700">; </span><span style="color: #FF8000">// sets $a to 8, as if we had said: $a = $a + 5;<br /></span><span style="color: #0000BB">$b </span><span style="color: #007700">= </span><span style="color: #DD0000">"Hello "</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$b </span><span style="color: #007700">.= </span><span style="color: #DD0000">"There!"</span><span style="color: #007700">; </span><span style="color: #FF8000">// sets $b to "Hello There!", just like $b = $b . "There!";<br /><br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">
Note that the assignment copies the original variable to the new
one (assignment by value), so changes to one will not affect the
other. This may also have relevance if you need to copy something
like a large array inside a tight loop.
</p>
<p class="para">
An exception to the usual assignment by value behaviour within PHP occurs
with <span class="type"><a href="language.types.object.html" class="type object">object</a></span>s, which are assigned by reference in PHP 5.
Objects may be explicitly copied via the <a href="language.oop5.cloning.html" class="link">clone</a> keyword.
</p>
<div class="sect2" id="language.operators.assignment.reference">
<h3 class="title">Assignment by Reference</h3>
<p class="para">
Assignment by reference is also supported, using the
"<span class="computeroutput">$var = &$othervar;</span>" syntax.
Assignment by reference means that both variables end up pointing at the
same data, and nothing is copied anywhere.
</p>
<p class="para">
<div class="example" id="example-117">
<p><strong>Example #1 Assigning by reference</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$a </span><span style="color: #007700">= </span><span style="color: #0000BB">3</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$b </span><span style="color: #007700">= &</span><span style="color: #0000BB">$a</span><span style="color: #007700">; </span><span style="color: #FF8000">// $b is a reference to $a<br /><br /></span><span style="color: #007700">print </span><span style="color: #DD0000">"</span><span style="color: #0000BB">$a</span><span style="color: #DD0000">\n"</span><span style="color: #007700">; </span><span style="color: #FF8000">// prints 3<br /></span><span style="color: #007700">print </span><span style="color: #DD0000">"</span><span style="color: #0000BB">$b</span><span style="color: #DD0000">\n"</span><span style="color: #007700">; </span><span style="color: #FF8000">// prints 3<br /><br /></span><span style="color: #0000BB">$a </span><span style="color: #007700">= </span><span style="color: #0000BB">4</span><span style="color: #007700">; </span><span style="color: #FF8000">// change $a<br /><br /></span><span style="color: #007700">print </span><span style="color: #DD0000">"</span><span style="color: #0000BB">$a</span><span style="color: #DD0000">\n"</span><span style="color: #007700">; </span><span style="color: #FF8000">// prints 4<br /></span><span style="color: #007700">print </span><span style="color: #DD0000">"</span><span style="color: #0000BB">$b</span><span style="color: #DD0000">\n"</span><span style="color: #007700">; </span><span style="color: #FF8000">// prints 4 as well, since $b is a reference to $a, which has<br /> // been changed<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">
As of PHP 5, the <a href="language.oop5.basic.html#language.oop5.basic.new" class="link">new</a>
operator returns a reference automatically, so assigning the result of
<a href="language.oop5.basic.html#language.oop5.basic.new" class="link">new</a> by reference results
in an <strong><code>E_DEPRECATED</code></strong> message in PHP 5.3 and later, and
an <strong><code>E_STRICT</code></strong> message in earlier versions.
</p>
<p class="para">
For example, this code will result in a warning:
<div class="informalexample">
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">class </span><span style="color: #0000BB">C </span><span style="color: #007700">{}<br /><br /></span><span style="color: #FF8000">/* The following line generates the following error message:<br /> * Deprecated: Assigning the return value of new by reference is deprecated in...<br /> */<br /></span><span style="color: #0000BB">$o </span><span style="color: #007700">= &new </span><span style="color: #0000BB">C</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">
More information on references and their potential uses can be found in
the <a href="language.references.html" class="link">References Explained</a>
section of the manual.
</p>
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