is_callable

(PHP 4 >= 4.0.6, PHP 5, PHP 7, PHP 8)

is_callable — Verify that a value can be called as a function from the current scope

Description

is_callable(mixed $value, bool $syntax_only = false, string &$callable_name = null): bool

Verifies that value is a callable, or that it can be called using the call_user_func() function.

Parameters

value

The value to be checked.

syntax_only

If set to true the function only verifies that value might be a function or method. It will reject any values that are not invokable objects, Closure, strings, or arrays that do not have a valid structure to be used as a callback. A valid callable array has 2 entries, the first of which is an object or a string, and the second a string.

callable_name

Receives the "callable name", e.g. "SomeClass::someMethod". Note, however, that despite the implication that SomeClass::someMethod() is a callable static method, this is not the case.

Return Values

Returns true if value is callable, false otherwise.

Examples

Example #1 Checking whether a string can be called as a function

<?php

function someFunction() {}

$functionVariable = 'someFunction';

var_dump(is_callable($functionVariable, false, $callable_name));

var_dump($callable_name);

?>

The above example will output:

bool(true)
string(12) "someFunction"

Example #2 Checking whether an array can be called as a function

<?php

class SomeClass
{
public function someMethod() {}
}

$anObject = new SomeClass();

$methodVariable = [$anObject, 'someMethod'];

var_dump(is_callable($methodVariable, true, $callable_name));

var_dump($callable_name);

?>

The above example will output:

bool(true)
string(21) "SomeClass::someMethod"

Example #3 is_callable() and constructors

Despite the fact that constructors are the methods that are called when an object is created, they are not static methods and is_callable() will return false for them. It's not possible to use is_callable() to check if a class can be instantiated from the current scope.

<?php

class Foo
{
public function __construct() {}

public function foo() {}
}

var_dump(
is_callable(['Foo', '__construct']),
is_callable(['Foo', 'foo'])
);

$foo = new Foo();
var_dump(is_callable([$foo, '__construct']));

?>

The above example will output:

bool(false)
bool(false)
bool(true)

Notes

  • An object is always callable if it implements __invoke(), and that method is visible in the current scope.
  • A class name is callable if it implements __callStatic().
  • If an object implements __call(), then this function will return true for any method on that object, even if the method is not defined.
  • This function may trigger autoloading if called with the name of a class.

See Also