f# - 在 F# 中添加额外的方法作为类型扩展

Question

我有一个已经实现的 .Net 库 .Item方法，例如

namespace Library2
type A() = 
    member m.Item with get(a: string) =   printfn "get a string"
    member m.Item with get(a: int) =   printfn "simple slice"

在使用这个库的代码中，我想添加一个额外的同名方法(因此它是 optional extensions ):

#r @"Library2.dll"
open Library2
type A with
    member m.Item with get(a: bool) =
        printfn "get a bool"

以下示例的最后一行无法编译:

let a = new A()
a.["good"]    
a.[10]
a.[true]

F# doc说:

Extension methods cannot be virtual or abstract methods. They can overload other methods of the same name, but the compiler gives preference to non-extension methods in the case of an ambiguous call.

这意味着我不能扩展 .ToString/.GetHashCode具有相同的类型签名，但在这里我使用了不同的类型签名。为什么不能扩展新方法？

Answer 1

我认为，问题是由扩展方法实现如下(C#)引起的:

public static class MyModule
{
    public static void Item(this A a, bool b)
    {
        // whatever
    }
}

编译器正在寻找 .Item(...)方法，在原 Library2.A中找到类，并且无法搜索任何扩展方法。

请注意，如果所有 .Item(...)重载是扩展方法，一切正常:

module Library2 =
    type A() = 
        member m.dummy = ()

open Library2
type A with
    member m.Item with get(a: string) =   printfn "get a string"
    member m.Item with get(a: int) =   printfn "simple slice"
    member m.Item with get(a: bool) = printfn "get a bool"