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

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

• 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.

<?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"; 
} 
  
?>

Yes

$a instanceof MyClass

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

<?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";
}

?>

Yes

• 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;