f# - 如何正确覆盖受约束的方法

Question

如何覆盖方法 Zero在下面的代码中，我可以返回 Euro(0)用于 type Euro 中的定义

[<AbstractClass>] 
type Currency () =
    abstract member Zero<'T when 'T :> Currency > : unit -> 'T

type Euro (value: int) =
    inherit Currency()
    member this.Value = value
    override this.Zero() = Euro(0) :> _

Answer 1

您是否尝试将通用约束提升到类级别？

[<AbstractClass>] 
type Currency<'T when 'T :> Currency<'T>>() =
    abstract member Zero : unit -> 'T

type Euro (value: int) =
    inherit Currency<Euro>()
    member this.Value = value
    override this.Zero() = Euro(0)

虽然自引用泛型对我来说总是很奇怪，但这就是它在例如 C# 中的实现方式。