is_callable in PHP

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

Syntax: bool is_callable ( callable $name [, bool $syntax_only = false [, string &$callable_name ]] )
Verify that the contents of a variable can be called as a function. 
This can check that a simple variable contains the name of a valid function, or that an array contains a properly encoded object and function name.
Parameters: 
name:The callback function to check
syntax_only
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:
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:
Returns TRUE if name is callable, FALSE otherwise.
Example #1
<?php
//  How to check a variable to see if it can be called
//  as a function.

//
//  Simple variable containing a function
//

function someFunction() 
{
}

$functionVariable = 'someFunction';

var_dump(is_callable($functionVariable, false, $callable_name));  // bool(true)

echo $callable_name, "\n";  // someFunction

//
//  Array containing a method
//

class someClass {

  function someMethod() 
  {
  }

}

$anObject = new someClass();

$methodVariable = array($anObject, 'someMethod');

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

echo $callable_name, "\n";  //  someClass::someMethod

?>