PHP function is_callable()

Version availability: PHP 4.0.6

Verify that the contents of a variable can be called as a function

Parameters

Parameter	Data type	Default value	Note
$name	`callback	callable`	not
$syntax_only	bool	null,	If set to true the function only verifies that name might be a function or method. It will only reject simple variables that are not strings, or an array that does not have a valid structure to be used as a callback. The valid ones are supposed to have only 2 entries, the first of which is an object or a string, and the second a string.
$callable_name	string	null	Receives the "callable name". In the example below it is "someClass::someMethod". Note, however, that despite the implication that someClass::SomeMethod() is a callable static method, this is not the case.

Return values

bool

true if name is callable, false otherwise.

Other resources

Official is-callable documentation