Question

我正在使用Argu解析cli参数。我注意到我需要为两个不同的事物使用相同的参数。我想使用相同的类型，只更改接口实现（我的Argument Discriminated Union上的IArgParserTemplate）。

与此类似的东西：

type IArgumentDescription =
     abstract member FirstDescription: string

type ImportArguments =
    interface IArgumentDescription with
        member this.FirstDescription = "Import Description"

type ExportArguments =
    interface IArgumentDescription with
        member this.FirstDescription = "Export Description"

type Arguments<'T when 'T :> IArgumentDescription> = | FirstArgument of string
with 
    interface IArgParserTemplate with
        member this.Usage =
            match this with
            | FirstArgument _ -> ? (Here I would like to use the 'T.FirstDescription of the IArgumentDescription Interface. (this:>IArgumentDescription).FirstDescription does not work.)

在FSharp中这是否可能，如果是，正确的语法是什么？

Answer 1

我想不出一个很好的方法，因为您不能真正地对一个被区分的联合进行参数化或“子类化”。您可能会使用涉及反射的肮脏技巧，但我不确定这是明智的选择（就像大多数与生产代码中反射相关的事情一样）。

type IArgParserTemplate =
    abstract member Usage : string


type IArgumentDescription =
     abstract member FirstDescription: string

// The parentheses are important to make this a class, not an interface
type ImportArguments() =
    interface IArgumentDescription with
        member this.FirstDescription = "Import Description"

// The parentheses are important to make this a class, not an interface
type ExportArguments() =
    interface IArgumentDescription with
        member this.FirstDescription = "Export Description"

type Arguments<'T when 'T :> IArgumentDescription> = | FirstArgument of string
with 
    interface IArgParserTemplate with
        member this.Usage =
            // Here's your instance of 'T
            let instance = Activator.CreateInstance<'T>()

            match this with
            | FirstArgument _ -> instance.FirstDescription

与歧视联盟上的另一个接口的成员实现接口

1 个答案: