language/oop5/static.xml
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3c831023489be0c64268882d5b656149140d6f8b
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This page describes the use of the <literal>static</literal> keyword to
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define static methods and properties. <literal>static</literal> can also
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be used to
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<link linkend="language.variables.scope.static">define static variables</link>
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<link linkend="language.variables.scope.static">define static variables</link>,
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<link linkend="functions.anonymous-functions.static">define static anonymous functions</link>
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and for
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<link linkend="language.oop5.late-static-bindings">late static bindings</link>.
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Please refer to those pages for information on those meanings of
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<para>
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Declaring class properties or methods as static makes them accessible
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without needing an instantiation of the class. A property declared as
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static cannot be accessed with an instantiated class object (though
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a static method can).
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</para>
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<para>
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For compatibility with PHP 4, if no <link
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linkend="language.oop5.visibility">visibility</link>
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declaration is used, then the property or method will be treated
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as if it was declared as <literal>public</literal>.
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without needing an instantiation of the class.
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These can also be accessed statically within an instantiated class object.
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</para>
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<sect2 xml:id="language.oop5.static.methods">
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<para>
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Because static methods are callable without an instance of
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the object created, the pseudo-variable <varname>$this</varname> is
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not available inside the method declared as static.
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not available inside methods declared as static.
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</para>
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<caution>
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<simpara>
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In PHP 5, calling non-static methods statically generates an
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<constant>E_STRICT</constant> level warning.
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</simpara>
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</caution>
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<warning>
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<simpara>
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In PHP 7, calling non-static methods statically is deprecated, and will
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generate an <constant>E_DEPRECATED</constant> warning. Support for
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calling non-static methods statically may be removed in the future.
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</simpara>
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<para>
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Calling non-static methods statically throws an <classname>Error</classname>.
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</para>
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<para>
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Prior to PHP 8.0.0, calling non-static methods statically were deprecated, and
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generated an <constant>E_DEPRECATED</constant> warning.
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</para>
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</warning>
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<example>
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Foo::aStaticMethod();
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$classname = 'Foo';
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$classname::aStaticMethod(); // As of PHP 5.3.0
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$classname::aStaticMethod();
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?>
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]]>
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</programlisting>
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<title>Static properties</title>
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<para>
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Static properties cannot be accessed through the object using the arrow
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operator ->.
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</para>
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<para>
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Like any other PHP static variable, static properties may only be
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initialized using a literal or constant before PHP 5.6; expressions are
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not allowed. In PHP 5.6 and later, the same rules apply as &const;
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expressions: some limited expressions are possible, provided they can be
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evaluated at compile time.
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Static properties are accessed using the
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<link linkend="language.oop5.paamayim-nekudotayim">Scope Resolution Operator</link>
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(<literal>::</literal>) and cannot be accessed through the object operator
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(<literal>-></literal>).
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</para>
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<para>
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As of PHP 5.3.0, it's possible to reference the class using a variable.
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It's possible to reference the class using a variable.
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The variable's value cannot be a keyword (e.g. <literal>self</literal>,
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<literal>parent</literal> and <literal>static</literal>).
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</para>
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print $foo::$my_static . "\n";
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$classname = 'Foo';
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print $classname::$my_static . "\n"; // As of PHP 5.3.0
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print $classname::$my_static . "\n";
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print Bar::$my_static . "\n";
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$bar = new Bar();
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?>
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]]>
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</programlisting>
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&example.outputs.8.similar;
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<screen>
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<![CDATA[
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foo
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foo
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Notice: Accessing static property Foo::$my_static as non static in /in/V0Rvv on line 23
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Warning: Undefined property: Foo::$my_static in /in/V0Rvv on line 23
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foo
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foo
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foo
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foo
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]]>
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</screen>
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</example>
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</sect2>
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</sect1>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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