在F#接口定义中实现???

问题描述

因此，我是F#的新手，并且阅读了一些不同的教程，而我惊讶地发现它提到F#接口定义实际上可以包括成员方法的默认实现(使它们像虚拟方法一样工作). .  提到 都在这里:

So I'm new to F#, and reading a couple of different tutorials, and I was surprised to see it mentioned that F# interface definitions can actually include default implementations for member methods (making them act like virtual methods).  This is mentioned both here:

http://www.tutorialspoint.com/fsharp/fsharp_interfaces.htm

http://www.tutorialspoint.com/fsharp/fsharp_interfaces.htm

在这里:

https://msdn.microsoft.com/zh-cn/visualfsharpdocs/conceptual/interfaces-%5Bfsharp%5D

https://msdn.microsoft.com/en-us/visualfsharpdocs/conceptual/interfaces-%5Bfsharp%5D

我发现这很奇怪，因为接口的定义特征之一是它不包含任何实现.  但是更奇怪的是，我似乎无法在网络上的任何地方找到更多有关此的信息.  我链接的那两个页面 仅提及这是可能的，但不赘述或提供任何示例.

I find this rather odd as one of the defining characteristics of an interface is that it contains no implementation.  But what's even more odd, is that I can't seem to find any more information on this anywhere on the web.  Those two pages I link merely mention that this is a possibility, but don't go into any detail or provide any examples.

那么这是如何工作的?  如果我提供了接口函数的默认实现，它将如何使用?  在类中实现接口时是否可以简单地忽略实现该方法，而将使用默认实现?  我可以使用base关键字直接从覆盖实现中调用默认实现吗?  如果我在F#中定义了这样的接口，然后尝试在C#类定义中实现它，会发生什么?  任何为此建立的用例 行为?

So how does this work?  If I provide a default implementation for an interface function, how does it get used?  Can I simply neglect to implement that method when implementing the interface in a class and the default implementation will be used?  Can I call the default implementation directly from my override implementation with the base keyword?  What happens if I define such an interface in F#, then try to implement it in a C# class definition?  Any established use cases for this behavior?

为什么没有在任何地方讨论这些内容?

And why isn't any of this discussed anywhere???

推荐答案

尝试(在F#3.0、3.1和4.0中)

Trying (in F# 3.0, 3.1 and 4.0)

type IPrintable = interface
   abstract member Print : unit -> unit
   default this.Print () = printfn "Hello, world!"
end

type SomeClass1(x: int, y: float) =
   interface IPrintable with
      member this.Print() = printfn "%d %f" x y

type SomeClass2() =
    member this.Action () = printfn "act"
    interface IPrintable

let x1 = new SomeClass1(1, 2.0)
(x1 :> IPrintable).Print()

let x2 = SomeClass2()
(x2 :> IPrintable).Print()

System.Console.ReadKey() |> ignore

收益

     default this.Print () = printfn "Hello, world!"
  ----------------^^^^^

stdin(5,17): error FS0867: Interfaces cannot contain definitions of member overrides

将IPrintable的定义更改为

Changing the definition of IPrintable to

type IPrintable =
   abstract member Print : unit -> unit
   default this.Print () = printfn "Hello, world!"

改为定义一个抽象类，我们得到

defines an abstract class instead, and we get

     interface IPrintable with
  -------------^^^^^^^^^^

stdin(30,14): error FS0887: The type 'IPrintable' is not an interface type

符合消费者的期望.

as expected from the consumers.

这篇关于在F#接口定义中实现???的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！