A delegate represents a function call as an object. A delegate is a reference type variable that holds the reference to a method. The reference can be changed at runtime.
The basic syntax of Delegate in F# is as follows.
type delegate-typename = delegate of type1 -> type2
The type1 represents the argument type or types, and type2 represents the return type. The argument types that are represented by type1 are automatically curried.
The following code shows a simple usage of a delegate.
type Deligate() =
static member add(a : int, b : int) =
a + b
member x.Add(a : int, b : int) =
a + b
type Multiply = delegate of (int * int) -> int
let getIt (d : Multiply) (a : int) (b: int) =
d.Invoke(a, b)
let d : Multiply = new Multiply( Deligate.add )
for (a, b) in [(5, 8) ] do
printfn "%d + %d = %d" a b (getIt d a b)
The following code shows some of the different ways you can work with delegates.
type Delegate1 = delegate of int * char -> string
let replicate n c = String.replicate n (string c)
let function1 = replicate
let delObject = Delegate1(function1)
let functionValue = delObject.Invoke
List.map (fun c -> functionValue(5,c)) ['a'; 'b'; 'c']|> List.iter (printfn "%s")
let replicate' n c = delObject.Invoke(n,c)
let stringArray = System.Array.ConvertAll([|'a';'b'|], fun c -> replicate' 3 c)
printfn "%A" stringArray