f# - 通过对象表达式扩展具有接口(interface)的对象

Question

是否可以使用对象表达式在 F# 中使用接口(interface)装饰对象。例如。:

type IFoo = abstract member foo : string
type IBar = abstract member bar : string
let a = { new IFoo with member x.foo = "foo" }

/// Looking for a variation on the below that does compile, the below doesn't
let b = { a with
             interface IBar with
                 member x.Bar = "bar" }

Answer 1

您不能在运行时使用接口(interface)扩展对象，但可以用另一个对象包装它:

let makeB (a: IFoo) = 
    { 
        new IFoo with
            member x.foo = a.foo
        interface IBar with
            member x.bar = "bar" 
    }


let a = { new IFoo with member x.foo = "foo" }
let b = makeB a