扩展F#列表模块

Question

我一直在为一些F#模块添加一些方便的方法,比如List.

type Microsoft.FSharp.Collections.FSharpList<'a> with          //'
    static member iterWhile (f:'a -> bool) (ls:'a list) = 
        let rec iterLoop f ls = 
            match ls with
            | head :: tail -> if f head then iterLoop f tail
            | _ -> ()
        iterLoop f ls

我想知道是否可以添加突变？我知道List是不可变的,那么如何向Ref类型List添加一个可变方法.像这样的东西.

type Ref<'a when 'a :> Microsoft.FSharp.Collections.FSharpList<'a> > with //'
    member this.AppendMutate element =
        this := element :: !this

或者是否有某种方法来约束泛型只接受一个可变的？

Answer 1

F# 3.1 中现在提供了通用扩展方法：

open System.Runtime.CompilerServices

[<Extension>]
type Utils () =
    [<Extension>]
    static member inline AppendMutate(ref: Ref<List<'a>>, elt) = ref := elt :: !ref

let ls = ref [1..10]

ls.AppendMutate(11)

printfn "%A" ls