Delegate declarations

Delegates give a name to a function signature. Use one when an API accepts, stores, or publishes callbacks that should share a distinct named type.

delegate Transformer(value: int) -> string

class Pipeline {
    delegate Stage<T>(ref value: T) -> bool
}

A delegate value can refer to a compatible named function, method, or function expression:

delegate Transformer(value: int) -> string

func format(value: int) -> string => "Value: $value"

let named: Transformer = format
let inline: Transformer = value => value.ToString()

If the return type is omitted, the delegate returns unit:

delegate Changed(value: int)

Delegate declarations may be generic and use the same constraints as other type declarations. Parameters retain their ref, out, in, and scoped modifiers.

At namespace scope, delegates default to internal; use public to export one from the assembly. A delegate nested inside another type defaults to public.

.NET representation

Delegates are emitted as sealed, abstract types derived from System.MulticastDelegate. For every declaration, the compiler provides:

• A constructor .ctor(object, IntPtr) that binds a target and method pointer.
• An Invoke method whose parameters (including any ref/out/in modifiers) and return type match the declaration.

The generated Invoke method preserves parameter lifetime metadata. In particular, scoped parameters emit ScopedRefAttribute when required, including parameters whose generic types permit ref-like arguments.