結構相等的F＃

Question

我有一個包括功能的記錄類型：

{foo : int; bar : int -> int} 

我想這種類型的有結構相等。有什麼方法可以標記在平等測試中bar應該被忽略嗎？或者還有其他解決方法嗎？

Answer 1

請參閱Don的blog關於此主題的帖子，具體爲自定義平等和比較。

他給出的例子幾乎是相同的，你提出的記錄結構：

/// A type abbreviation indicating we’re using integers for unique stamps on objects 
type stamp = int 

/// A type containing a function that can’t be compared for equality 
[<CustomEquality; CustomComparison>] 
type MyThing = 
    { Stamp: stamp; 
     Behaviour: (int -> int) } 

    override x.Equals(yobj) = 
     match yobj with 
     | :? MyThing as y -> (x.Stamp = y.Stamp) 
     | _ -> false 

    override x.GetHashCode() = hash x.Stamp 
    interface System.IComparable with 
     member x.CompareTo yobj = 
      match yobj with 
      | :? MyThing as y -> compare x.Stamp y.Stamp 
      | _ -> invalidArg "yobj" "cannot compare values of different types" 

Answer 2

要回答更具體的你原來的問題，您可以創建一個自定義類型的實例之間，其對比始終是真實的：

[<CustomEquality; NoComparison>] 
type StructurallyNull<'T> = 
    { v: 'T } 

    override x.Equals(yobj) = 
     match yobj with 
     | :? StructurallyNull<'T> as y -> true 
     | _ -> false 

    override x.GetHashCode() = 0 

type MyType = { 
    foo: int; 
    bar: StructurallyNull<int -> int> 
}