如何在F中集中定义抽象(接口)类型上的IComparable#

这个问题是下一个层次的问题 F# Set using custom class --我想为泛型接口定义IComparable。

我有一组实现共享元数据交换接口的任意类型, ITree 伊特雷

我意识到这些东西并不完全是惯用的F#,但我正在尝试与现有的C#和VB代码进行互操作,因此我希望尽可能使用.NET接口和比较。

open System
open System.Collections.Generic

// Simplified "generic" metadata type that all implementers agree on
type ITree =
  abstract Path: string with get, set
  abstract ModifyDate: DateTime with get, set

type Thing1(path, date) =
  interface ITree with
    member x.Path = path
    member x.ModifyDate = date

// In reality, the types implementing ITree are going to
// come from different external assemblies
type Thing2(path, date) =
  interface ITree with
    member x.Path = path
    member x.ModifyDate = date

let d1 = DateTime.Now
let d2 = DateTime.Now.AddMinutes(-2.0)
let xs : seq<ITree> = Seq.cast [ Thing1("/stuff", d1); Thing1("/dupe", d1); Thing1("/dupe", d1) ]
let ys : seq<ITree> = Seq.cast [ Thing2("/stuff", d2); Thing2("/dupe", d1) ]

// Then I would like to take advantage of F# Sets
// to do comparison across these things
let xset = Set.ofSeq xs
let yset = Set.ofSeq ys

let same = Set.intersect xset yset
let diffs = (xset + yset) - same

现在实际的问题是:这不会编译,因为 伊特雷 还没有实现 IComparable . 我需要一个自定义的比较,有助于时钟歪斜,最终其他事情。

有没有办法定义比较函数 伊特雷 直接地

如果我试着去做

type ITree =
  abstract Path: string with get, set
  abstract ModifyDate: DateTime with get, set
    interface IComparable<ITree> with
      let Subtract (this: ITree) (that: ITree) =
        this.ModifyDate.Subtract(that.ModifyDate)
      match compare (this.Path, this.ParentPath) (that.Path, this.ParentPath) with
      | 0 ->
        // Paths are identical, so now for a stupid timespan comparison
        match abs (Subtract this that).TotalSeconds with
        | x when x > 60.0  -> int x
        | _ -> 0
      | x -> x

编译器认为 伊特雷 不再是一个抽象的接口,或是令人困惑的东西。

IComparer<T> 喜欢

type ITreeComparer =      
  interface IComparer<ITree> with
    member x.Compare(this, that) = ...

但是我不知道该怎么说 Set... 使用该IComparer的函数。

(我假设一旦我弄明白如何申请 IComparer<T> IEqualityComparer<T> 根据需要。)

编辑: 我能行

let x = new HashSet<ITree>(a |> Seq.cast<ITree>, new ITreeEqualityComparer())

使用普通的.NET集合,这应该足以解决此问题;然而,我仍然想知道是否有更好的方法来做我想做的事情。