F# -> 为 HashSet<'a> 实现 IComparable

Question

是否有可能以某种方式实现 IComparable对于 HashSet<'a> ?原因是我声明了以下记录:

[<StructuralComparison>]
type Category = { 
    mutable Id: string; 
    Name: string; 
    SavePath: string;
    Tags: HashSet<Tag> }

and Tag = { Tag:string; }

如您所见，然后在 Category 中添加标签记录类型为 HashSet<Tag> - 为了将一系列类别映射到 map ，我需要实现 IComparable不知何故......否则它只会导致:

The struct, record or union type 'Category' has the 'StructuralComparison' attribute but the component type 'HashSet' does not satisfy the 'comparison'

请注意，除了 HashSet<'a> 我不能使用其他任何东西因为我正在使用的数据库完全理解任何 fsharp-ish 列表。

Answer 1

我假设你想比较和等同 Category s 只服用 Id , Name , 和 SavePath考虑到(按该顺序)，使记录表现得好像 Tags不在场:

open System
open System.Collections.Generic

[<CustomComparison; CustomEquality>]
type Category =
    { mutable Id : string;
      Name       : string;
      SavePath   : string;
      Tags       : HashSet<Tag> }
    member private this.Ident = this.Id, this.Name, this.SavePath
    interface IComparable<Category> with
        member this.CompareTo other =
            compare this.Ident other.Ident
    interface IComparable with
        member this.CompareTo obj =
            match obj with
              | null                 -> 1
              | :? Category as other -> (this :> IComparable<_>).CompareTo other
              | _                    -> invalidArg "obj" "not a Category"
    interface IEquatable<Category> with
        member this.Equals other =
            this.Ident = other.Ident
    override this.Equals obj =
        match obj with
          | :? Category as other -> (this :> IEquatable<_>).Equals other
          | _                    -> false
    override this.GetHashCode () =
        hash this.Ident

and Tag = { Tag : string; }

但是，如果您想通过 Name 进行比较并等于 Id然后考虑以下事项:

open System
open System.Collections.Generic

[<CustomComparison; CustomEquality>]
type Category =
    { mutable Id : string;
      Name       : string;
      SavePath   : string;
      Tags       : HashSet<Tag> }
    interface IComparable<Category> with
        member this.CompareTo { Name = name } =
            this.Name.CompareTo name
    interface IComparable with
        member this.CompareTo obj =
            match obj with
              | null                 -> 1
              | :? Category as other -> (this :> IComparable<_>).CompareTo other
              | _                    -> invalidArg "obj" "not a Category"
    interface IEquatable<Category> with
        member this.Equals { Id = id } =
            this.Id = id
    override this.Equals obj =
        match obj with
          | :? Category as other -> (this :> IEquatable<_>).Equals other
          | _                    -> false
    override this.GetHashCode () =
        this.Id.GetHashCode ()

and Tag = { Tag : string; }