What is the difference between is_a() function and instanceof in PHP?

is_a() Function
The is_a() is a built-in function in PHP which is used to check whether a given object is of a given class or not. It also checks if the given class is one of the parents of the given object or not.

Syntax:

bool is_a( $object, $class_name, $allow_string )

Parameters: This function accepts three parameters as mentioned above and described below:

• object: This parameter is used to hold the tested object.
• class_name: This parameter is used to hold the class name.
• allow_string: If this parameter set to False, string class name as object is not allowed.

Return Value : This function 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.

Below programs illustrate the is_a() function:

<?php
// PHP program to illustrate the
// is_a() function

// sample class
class GeeksforGeeks {
    var $store = 'Hello geeks!';
}

// create a new object
$geek = new GeeksforGeeks();

// checks if $geek is an object
// of class GeeksforGeeks
if (is_a($geek, 'GeeksforGeeks')) {
    echo "Yes";
}

?>

Output:

Yes

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

Syntax:

$a instanceof MyClass

Operands: This operator contains two operands which are listed below:

• $a: This is used as an object.
• MyClass: It is a 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.

Below programs illustrate the instanceof operator in PHP:

<?php
// PHP program to illustrate instanceof
// operator

// sample class
class GeeksforGeeks {
    var $store = 'Hello geeks!';
}

// create a new object
$geek = new GeeksforGeeks();

// Checks if $geek is an object of
// class GeeksforGeeks
if ($geek instanceof GeeksforGeeks) {
    echo "Yes";
}

?>

Output:

Yes

Difference between is_a() function and instanceof operator:

• The is_a() is a function, whereas instanceof is a language construct. The is_a() function will be significantly slower since it has all the overhead of executing a function call.
• In case of callback in functions (like array_map) instanceof is not a function, it is a language construct, so it cannot use as callback. On the other hand callback can be used in is_a() function.
• The use of direct class name with instanceof is shorter than is_a() function.
  Example:

  // Short syntax (comparatively)
  $a instanceof MyClass
  
  is_a( $a, MyClass::class )
  

• The is_a() being a function takes an object as parameter one, and a string as parameter two, whereas instanceof takes an object as parameter one, and can take a class name, object instance, or class identifier (class name written without quotes) as parameter two.

  Example of is_a():

  // Only way to call it
  is_a( $object, $string );
  

  Example of instanceof:

  // Object instance      
  $object instanceof $otherObject; 
  
  // String class name
  $object instanceof $string;
  
  // Identifier for the class
  $object instanceof ClassName;