PHP | Check if a variable is a function

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    // 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    // Declare a variable and initialize // with function $func = function() {      echo 'neveropen';  };    // Use instanceof to check it contains // function or not if($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    // Declare a function function myFun() {      echo 'neveropen';  };     // 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:

  1