Skip to main content

instanceof

The instanceof keyword performs a runtime type test. It returns true when the value on the left is an instance of (or a subtype of) the type on the right, and false otherwise.

Syntax & Example​

let shape: Shape = Circle { radius: 2.0 };

if shape instanceof Circle {
    print("it is a circle");
}

Use Cases​

  • Checking the dynamic type of a value before downcasting.
  • Guarding branches that depend on a specific runtime subtype.
  • Distinguishing instanceof (runtime check) from typeof (compile-time query).