PHP | is_callable() Function

The is_callable() function is an inbuilt function in PHP which is used to verify the contents of a variable can be called as a function. It 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.

Syntax:

bool is_callable ( $variable_name, $syntax_only, $callable_name )

Parameters: The is_callable() function accepts three parameters as shown in above syntax and are described below. It depends on user to use how many parameters one, two or three.

• $variable_name: The name of a function stored in a string variable $variable_name, or an object and the name of a method within the object.
• $syntax_only: If set to TRUE the function only verifies that name might be a function or method. It will 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. This option only implemented for classes.

Return value: This function returns a boolean type value. It returns TRUE if $variable_name is callable, FALSE otherwise.

Below program illustrate the is_callable() function in PHP:
Program 1: Simple variable contains a function

<?php
// To check a variable if it can be called
// as a function.

// Declare the function
function Function_xyz()
{
}

$variable_name = "Function_xyz";
var_dump(is_callable($variable_name, false, $callable_name));
echo $callable_name, "\n";

// using only-one parameter
var_dump(is_callable($variable_name));
?>

Output:

bool(true)
Function_xyz
bool(true)

Program 2: Array contains a method

<?php
// To check a variable if it can be called
// as a function.

// Define class
class ClassA {
   // Define method
  function Method_xyz()
  {
  }

}

// Object instance
$obj = new ClassA();

$variable_name = array($obj, 'Method_xyz');

var_dump(is_callable($variable_name, true, $callable_name));
echo $callable_name, "\n";
?>

Output:

bool(true)
ClassA::Method_xyz

Reference: http://php.net/manual/en/function.is-callable.php