PHP | Check if a variable is a function

Last Updated : 05 Mar, 2019

To determine whether a passed argument is a function or not, Few of the most preferred methods are shown below.

Using is_callable() Function: It is an inbuilt function in PHP which is used to verify the contents of a variable in 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 ( $var_name, $syntx_only, $calbl_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.
- $var_name: The name of a function stored in a string variable $var_name, or an object and the name of a method within the object.
- $syntx_only: If it 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.
- $calbl_name: It receives the callable name. This option only implemented for classes.
Return Value: This function returns a boolean type value. It returns TRUE if $var_name is callable, FALSE otherwise. Example: This example uses is_callable() function to verify whether the parameter is a function or not.
php
<?php // Declare a variable and initialize // with function $function = function() { echo 'GeeksForGeeks'; }; // Check is_callable function contains // function or not if( is_callable( $function ) ) { echo "It is function"; } else { echo "It is not function"; } // Declare a variable and // initialize it $var = "GeeksForGeeks"; echo "\n"; // Check is_callable function contains // function or not if( is_callable( $var ) ) { echo "It is function"; } else { echo "It is not function"; } ?>
Output:
```
It is function
It is not function
```

instanceof: The instanceof operator in PHP is used to find out if an object is an instantiated instance of a class. Syntax:

$f instanceof Class_Name

Operands: It contains two operands which are listed below:

$f: It is used as an object.
Class_Name: It is used to hold the class name.

Return Value: It returns True if the object is of this class or has this class as one of its parents else it will return a False value. Example: This example use instanceof operator to determine if a variable is a function in PHP.

php

<?php

// Declare a variable and initialize
// with function
$func = function() { 
    echo 'GeeksforGeeks'; 
};

// Use instanceof to check it contains
// function or not
if($func instanceof Closure) {
    echo "function";
}
else {
    echo "not a function";
}

// Declare a variable and initialize it
$var = "GFG";
echo "\n";

// Use instanceof to check it contains
// function or not
if($var instanceof Closure) {
    echo "function";
}
else{
    echo "not a function";
}
?>

Output:

function
not a function

Example: This example uses function_exist() and is_object() methods to check whether an argument is a function or not.

php

<?php

// Declare a function
function myFun() { 
    echo 'GeeksforGeeks'; 
}; 

// Determine if a variable is a function
function is_function($func) {
    return (is_string($func) && function_exists($func)) 
    || (is_object($func) && ($func instanceof Closure));
}

echo is_function('myFun');

?>

Output:

PHP | Check if a variable is a function

PranchalKatiyar

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