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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision: 326724 $ -->
<sect1 xml:id="language.oop5.static" xmlns="http://docbook.org/ns/docbook">
<title>Static Keyword</title>
<tip>
<simpara>
This page describes the use of the <literal>static</literal> keyword to
define static methods and properties. <literal>static</literal> can also
be used to
<link linkend="language.variables.scope.static">define static variables</link>
and for
<link linkend="language.oop5.late-static-bindings">late static bindings</link>.
Please refer to those pages for information on those meanings of
<literal>static</literal>.
</simpara>
</tip>
<para>
Declaring class properties or methods as static makes them accessible
without needing an instantiation of the class. A property declared as
static can not be accessed with an instantiated class object (though
a static method can).
</para>
<para>
For compatibility with PHP 4, if no <link
linkend="language.oop5.visibility">visibility</link>
declaration is used, then the property or method will be treated
as if it was declared as <literal>public</literal>.
</para>
<para>
Because static methods are callable without an instance of
the object created, the pseudo-variable <varname>$this</varname> is
not available inside the method declared as static.
</para>
<para>
Static properties cannot be accessed through the object using the arrow
operator ->.
</para>
<para>
Calling non-static methods statically generates an <constant>E_STRICT</constant> level warning.
</para>
<para>
Like any other PHP static variable, static properties may only be
initialized using a literal or constant; expressions are not
allowed. So while you may initialize a static property to an
integer or array (for instance), you may not initialize it to
another variable, to a function return value, or to an object.
</para>
<para>
As of PHP 5.3.0, it's possible to reference the class using a variable.
The variable's value can not be a keyword (e.g. <literal>self</literal>,
<literal>parent</literal> and <literal>static</literal>).
</para>
<example>
<title>Static property example</title>
<programlisting role="php">
<![CDATA[
<?php
class Foo
{
public static $my_static = 'foo';
public function staticValue() {
return self::$my_static;
}
}
class Bar extends Foo
{
public function fooStatic() {
return parent::$my_static;
}
}
print Foo::$my_static . "\n";
$foo = new Foo();
print $foo->staticValue() . "\n";
print $foo->my_static . "\n"; // Undefined "Property" my_static
print $foo::$my_static . "\n";
$classname = 'Foo';
print $classname::$my_static . "\n"; // As of PHP 5.3.0
print Bar::$my_static . "\n";
$bar = new Bar();
print $bar->fooStatic() . "\n";
?>
]]>
</programlisting>
</example>
<example>
<title>Static method example</title>
<programlisting role="php">
<![CDATA[
<?php
class Foo {
public static function aStaticMethod() {
// ...
}
}
Foo::aStaticMethod();
$classname = 'Foo';
$classname::aStaticMethod(); // As of PHP 5.3.0
?>
]]>
</programlisting>
</example>
</sect1>
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