php check if variable is a class code example

Example 1: php instanceof

<?php
/*
 * 
 * opcode number: 138
 */
$obj = new A();

if ($obj instanceof A) {
   echo 'A';
}
?>

Example 2: how work instanceof php method

class MyClass {
}

$o1 = new MyClass();
$o2 = new MyClass();
$name = 'MyClass';

// in the cases below, $a gets boolean value true
$a = $o1 instanceof MyClass;
$a = $o1 instanceof $name;
$a = $o1 instanceof $o2;

// counter examples:
$b = 'b';
$a = $o1 instanceof 'MyClass'; // parse error: constant not allowed
$a = false instanceof MyClass; // fatal error: constant not allowed
$a = $b instanceof MyClass;    // false ($b is not an object)