F# and duck-typing

Question

Let\'s say I defined in F# the following two types:

type Dog = { DogName:string; Age:int }
type Cat = { CatName:string; Age:int }

I was exp

Answer 1

Usually what is meant by F# duck-typing is a compile-time polymorphism. Syntax is a little weirder, but you should be able to work it out from the following example -

module DuckTyping

// Demonstrates F#'s compile-time duck-typing.

type RedDuck =
    { Name : string }
    member this.Quack () = "Red"

type BlueDuck =
    { Name : string }
    member this.Quack () = "Blue"

let inline name this =
    (^a : (member Name : string) this)

let inline quack this =
    (^a : (member Quack : unit -> string) this)

let howard = name { RedDuck.Name = "Howard" }
let bob = name { BlueDuck.Name = "Bob" }
let red = quack { RedDuck.Name = "Jim" }
let blue = quack { BlueDuck.Name = "Fred" }

Remember, this polymorphism only works at compile-time!