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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<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>,
<link linkend="functions.anonymous-functions.static">define static anonymous functions</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.
These can also be accessed statically within an instantiated class object.
</para>
<sect2 xml:id="language.oop5.static.methods">
<title>Static methods</title>
<para>
Because static methods are callable without an instance of
the object created, the pseudo-variable <varname>$this</varname> is
not available inside methods declared as static.
</para>
<warning>
<para>
Calling non-static methods statically throws an <classname>Error</classname>.
</para>
<para>
Prior to PHP 8.0.0, calling non-static methods statically were deprecated, and
generated an <constant>E_DEPRECATED</constant> warning.
</para>
</warning>
<example>
<title>Static method example</title>
<programlisting role="php">
<![CDATA[
<?php
class Foo {
public static function aStaticMethod() {
// ...
}
}
Foo::aStaticMethod();
$classname = 'Foo';
$classname::aStaticMethod();
?>
]]>
</programlisting>
</example>
</sect2>
<sect2 xml:id="language.oop5.static.properties">
<title>Static properties</title>
<para>
Static properties are accessed using the
<link linkend="language.oop5.paamayim-nekudotayim">Scope Resolution Operator</link>
(<literal>::</literal>) and cannot be accessed through the object operator
(<literal>-></literal>).
</para>
<para>
It's possible to reference the class using a variable.
The variable's value cannot 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";
print Bar::$my_static . "\n";
$bar = new Bar();
print $bar->fooStatic() . "\n";
?>
]]>
</programlisting>
&example.outputs.8.similar;
<screen>
<![CDATA[
foo
foo
Notice: Accessing static property Foo::$my_static as non static in /in/V0Rvv on line 23
Warning: Undefined property: Foo::$my_static in /in/V0Rvv on line 23
foo
foo
foo
foo
]]>
</screen>
</example>
</sect2>
</sect1>
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