F＃：会员约束来帮助创建看似动态的类型 [英] F#: Member constraints to help create seemingly dynamic types

问题描述

我一直在寻找一种方法来为F＃方法添加一些鸭子打字。

I've been looking into a way to add some duck typing to an F# method.

SomeMethod(model:'a) =
   let someField = model.Test("")

其中的参数有Test方法。我见过这样的记法：

Where the parameter coming in has the Test method on it. I've seen notation like this:

member inline public x.Testing< ^a when ^a : (member public Test : String-> String)>(model:^a) =   
  let something = model.Test("")
  ignore

在我看来，通用约束可以用于方法级别而不是类/接口级别。问题是由于类型问题，我无法编译它。这使我相信，没有办法在方法级别指定约束。

Which looks like to me that generic constraints can be used to enfore at a method level rather than class/interface level. Problem is I can't get it to compile due to type issues. This leads me to believe that there isn't a way to specify constraints at the method level. Is that coorect?

推荐答案

这个语法有点笨拙，但在这里。

The syntax for this is a bit clunky, but here it is.

type Foo() =
  member inline public x.Testing(model) =   
    let something = (^a : (member Test : string -> string) (model, ""))
    ignore

重新使用接口可能会更好：

You're probably better off using an interface:

type IModel
  abstract Test : string -> string

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