這是一個F＃bug嗎？

Question

我有一個正在實施IEnumerable<T>接口的類型，一切正常：

open System 

type Bar() = 

    interface Collections.IEnumerable with 
     member x.GetEnumerator() = null 

    interface Collections.Generic.IEnumerable<int> with 
     member x.GetEnumerator() = null 

但如果類型繼承通過基本類型IEnumerable接口實現的東西出了問題：上面

open System 

type Foo() = 
    interface Collections.IEnumerable with 
     member x.GetEnumerator() = null 

type Bar() = 
    inherit Foo() 

    interface Collections.Generic.IEnumerable<int> with 
     member x.GetEnumerator() = null 

代碼生成型推理錯誤：

• The member 'GetEnumerator<'a0 when 'a0 : null> : unit -> 'a0 when 'a0 : null' does not have the correct type to override any given virtual method

• The member 'GetEnumerator<'a0 when 'a0 : null> : unit -> 'a0 when 'a0 : null' does not have the correct number of method type parameters. The required signature is 'GetEnumerator : unit -> Collections.Generic.IEnumerator<int>'.

我做得不對或這是F＃編譯器錯誤？

Microsoft (R) F# 2.0 Interactive build 4.0.30319.1

---

更新更典型的例子：

type IFoo  = abstract Bar : obj list 
type IFoo<'a> = abstract Bar : 'a list 
       inherit IFoo 
/* ok */ 
type Foo  = interface IFoo  with member x.Bar = [] 
        interface IFoo<Foo> with member x.Bar = [] 
/* fail */ 
type FooBase = interface IFoo  with member x.Bar = [] 
type FooDerived = interface IFoo<Foo> with member x.Bar = [] // <--- 
        inherit FooBase 
/* 
error FS0017: The member 'get_Bar : unit -> 'a list' does not 
    have the correct type to override any given virtual method. 
*/ 

Answer 1

這是不是一個錯誤，這只是一個類型推斷失敗，因爲F＃中派生的接口實現聲明可以實現繼承接口成員：

type IA = abstract A : int 
type IB = inherit IA 
type IC = inherit IB 

type Baz = 
    interface IC with 
     member x.A = 1 

所以在我的例子中，我應該指定正確的返回類型明確地因爲member x.GetEnumerator()派生的Bar類型可能匹配IEnumerable.GetEnumerator()和IEnumerable<T>.GetEnumerator()。

Answer 2

編譯器不能推斷出從 「空」 - 實施正確的類型。嘗試

open System 

type Foo() = 
    interface Collections.IEnumerable with 
     member x.GetEnumerator() = null 

type Bar() = 
    inherit Foo() 

    interface Collections.Generic.IEnumerable<int> with 
     member x.GetEnumerator() : Collections.Generic.IEnumerator<int> = null 

更新：
其原因是，由Bar類型實現的GetEnumerator方法的類型是ambigous作爲IEnumerable<'a>工具/繼承了非通用IEnumerable其還指定（非通用）GetEnumerator方法。那麼，編譯器應該如何推斷，如果他得到的所有內容都是null，那麼您正在試圖實現哪種方法？因此，在這種情況下我們需要一個類型註釋。