language/types/callable.xml
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c897161ca5a62a887295c695adc161b8fde5d772
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<title>Callbacks / Callables</title>
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<para>
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Callbacks can be denoted by <type>callable</type> type hint as of PHP 5.4.
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This documentation used <type>callback</type> type information for the same
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purpose.
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Callbacks can be denoted by the <type>callable</type> type declaration.
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</para>
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<para>
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<para>
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A method of an instantiated <type>object</type> is passed as an
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<type>array</type> containing an <type>object</type> at index 0 and the
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method name at index 1.
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method name at index 1. Accessing protected and private methods from
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within a class is allowed.
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</para>
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<para>
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Static class methods can also be passed without instantiating an
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<type>object</type> of that class by passing the class name instead of an
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<type>object</type> at index 0.
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As of PHP 5.2.3, it is also possible to pass
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<type>object</type> of that class by either, passing the class name
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instead of an <type>object</type> at index 0, or passing
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<literal>'ClassName::methodName'</literal>.
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</para>
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<para>
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Apart from common user-defined function,
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<link linkend="functions.anonymous">anonymous functions</link> can also be
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<link linkend="functions.anonymous">anonymous functions</link> and
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<link linkend="functions.arrow">arrow functions</link> can also be
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passed to a callback parameter.
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</para>
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<note>
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<para>
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As of PHP 8.1.0, anonymous functions can also be created using the <link linkend="functions.first_class_callable_syntax">first class callable syntax</link>.
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</para>
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</note>
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<para>
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Generally, any object implementing <link linkend="object.invoke">__invoke()</link> can also
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be passed to a callback parameter.
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</para>
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<para>
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<example>
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<title>
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$obj = new MyClass();
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call_user_func(array($obj, 'myCallbackMethod'));
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// Type 4: Static class method call (As of PHP 5.2.3)
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// Type 4: Static class method call
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call_user_func('MyClass::myCallbackMethod');
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// Type 5: Relative static class method call (As of PHP 5.3.0)
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// Type 5: Relative static class method call
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class A {
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public static function who() {
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echo "A\n";
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}
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}
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call_user_func(array('B', 'parent::who')); // A
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call_user_func(array('B', 'parent::who')); // A, deprecated as of PHP 8.2.0
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// Type 6: Objects implementing __invoke can be used as callables
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class C {
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public function __invoke($name) {
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echo 'Hello ', $name, "\n";
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}
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}
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$c = new C();
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call_user_func($c, 'PHP!');
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?>
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]]>
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</programlisting>
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</example>
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</para>
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<note>
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<simpara>
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In PHP 4, it was necessary to use a reference to create a callback that
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points to the actual <type>object</type>, and not a copy of it. For more
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details, see
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<link linkend="language.references">References Explained</link>.
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</simpara>
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</note>
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¬e.func-callback-exceptions;
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</sect2>
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