Decorators

A decorator is a function that either returns void or returns another function that returns void, applied to either a type, property or method as expressions enclosed by square brackets. Decorators cannot be applied everywhere.

[D(x = 10)] is equivalent to [D({x: 10})].

Note that 4 lexical names may be reserved in some contexts. Jump to the Reserved Lexical Decorators section below for quick information.

Decorators Applied to Types

function MyTypeDecorator(type: Class): void {
}

[MyTypeDecorator]
class C {
}

Decorators Applied to Properties

function MyFieldDecorator(o: C, {name}: Binding): void {
    trace(name);
}

class C {
    [MyFieldDecorator]
    public var x: Number;
}

Decorators Applied to Methods

function MyMethodDecorator(o: C, name: String): void {
    trace(name);
}

class C {
    [MyMethodDecorator]
    public function f(): void {
    }
}

Reserved Lexical Decorators

The following decorators are reserved, but can still be used if they do not directly appear as lexical references:

• [Metadata()]
• [Allow()]
• [Warn()]
• [FFI()]
• When applied to a class definition, [Value] is reserved
• When applied to a class definition, [DontInit] is reserved
• When applied to an enum definition, [Flags] is reserved

You can still use them if they are under a namespace or package, such as q.b.Metadata.