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 '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
  
  // 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:

  1