Expressions And Operators: Instanceof

The use of instanceof has been deprecated; use operator is instead.

Operator instanceof determines if the variable designated by its left-hand operand is an object having the type specified by the right-hand one. It returns a bool result. For example:

class C1 { ... }
class C2 { ... }
class D extends C1 { ... }
$d = new D();
$d instanceof C1      // true
$d instanceof C2      // false
$d instanceof D       // true

Variable $d has type D, and, by definition, every D is a C1, so $d is an instance of type C1. And clearly, it is an instance of its own type, D. However, it is not an instance of the completely unrelated type C2.

instanceof works equally well with interface types. For example:

interface I1 { ... }
interface I2 { ... }
class E1 implements I1 { ... }
$e1 = new E1();
$e1 instanceof I1     // true
$e1 instanceof I2     // false