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# Type Operators

`instanceof` is used to determine whether a PHP variable is an instantiated object of a certain class:

Example 15-7. Using instanceof with classes

`<?php class MyClass { } class NotMyClass { } $a = new MyClass; var_dump($a instanceof MyClass); var_dump($a instanceof NotMyClass); ?>`

The above example will output:

    bool(true)
    bool(false)

`instanceof` can also be used to determine whether a variable is an instantiated object of a class that inherits from a parent class:

Example 15-8. Using instanceof with inherited classes

`<?php class ParentClass { } class MyClass extends ParentClass { } $a = new MyClass; var_dump($a instanceof MyClass); var_dump($a instanceof ParentClass); ?>`

The above example will output:

    bool(true)
    bool(true)

Lastly, `instanceof` can also be used to determine whether a variable is an instantiated object of a class that implements an interface:

Example 15-9. Using instanceof for class

`<?php interface MyInterface { } class MyClass implements MyInterface { } $a = new MyClass; var_dump($a instanceof MyClass); var_dump($a instanceof MyInterface); ?>`

The above example will output:

    bool(true)
    bool(true)

Although `instanceof` is usually used with a literal classname, it can also be used with another object or a string variable:

Example 15-10. Using instanceof with other variables

`<?php interface MyInterface { } class MyClass implements MyInterface { } $a = new MyClass; $b = new MyClass; $c = 'MyClass'; $d = 'NotMyClass'; var_dump($a instanceof $b); // $b is an object of class MyClass var_dump($a instanceof $c); // $c is a string 'MyClass' var_dump($a instanceof $d); // $d is a string 'NotMyClass' ?>`

The above example will output:

    bool(true)
    bool(true)
    bool(false)

There are a few pitfalls to be aware of. Before PHP version 5.1.0, `instanceof` would call __autoload() if the class name did not exist. In addition, if the class was not loaded, a fatal error would occur. This can be worked around by using a `dynamic class reference`, or a string variable containing the class name:

Example 15-11. Avoiding classname lookups and fatal errors with instanceof in PHP 5.0

`<?php $d = 'NotMyClass'; var_dump($a instanceof $d); // no fatal error here ?>`

The above example will output:

    bool(false)

The `instanceof` operator was introduced in PHP 5. Before this time is_a() was used but is_a() has since been deprecated in favor of `instanceof`.

See also get_class() and is_a().

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