c# - 在 F# 中从 C# 实现接口(interface)并添加方法来更新对象属性(返回新实例)

Question

我在 C# 库中定义了以下接口(interface)

public interface IMatch
{
    string CompetitionId { get; }
    int MatchNumber { get; }
    MatchType Type { get; }
    SeriesType SeriesType { get; }
    bool Finished { get; }
}

然后我在我的 F# 库中创建了一个类型来实现这样的接口(interface)

type Match(
            competitionId: string,
            finished: bool,
            matchNumber: int,
            seriesType: SeriesType,
            matchType: MatchType) = 
interface IMatch with
    member this.Finished with get() = finished
    member this.MatchNumber with get() = matchNumber
    member this.SeriesType with get() = seriesType
    member this.Type with get() = matchType
    member this.CompetitionId with get() = competitionId

现在，我阅读了 this article我在 Person 类型上看到了 WithUpdatedEmail 方法:

type Person = {
    FirstName: string
    LastName: string
    Email: string
}

with member this.WithUpdatedEmail email = { this with Email = email }

调用该方法时，它将返回一个包含更新后的电子邮件的新 Person 实例。是否可以在我的 Match 类型上添加类似的方法？我尝试了以下但无法编译(记录标签 Finished 未定义)，我是 F# 的新手，所以请耐心等待这是不可能的……:)

type Match(
            competitionId: string,
            finished: bool,
            matchNumber: int,
            seriesType: SeriesType,
            matchType: MatchType) = 
interface IMatch with
    member this.Finished with get() = finished
    member this.MatchNumber with get() = matchNumber
    member this.SeriesType with get() = seriesType
    member this.Type with get() = matchType
    member this.CompetitionId with get() = competitionId

with member this.Finished finished = { this with Finished = finished}

Answer 1

Copy and update record expressions — 一个允许您编写 { rec with prop = val } — 是创建新记录的便捷快捷方式，只需对现有记录实例进行一些更改。

当然我可能是错的，但是 record 允许使用这种语法只有类型，而你已经声明了一个 Match class使用自定义构造函数，这不是记录。

所以您可能想改用记录。

type Match =
    { CompetitionId: string
      Finished: bool
      MatchNumber: int
      SeriesType: SeriesType
      MatchType: MatchType } 
    interface IMatch with
        member this.Finished with get() = this.Finished
        member this.MatchNumber with get() = this.MatchNumber
        member this.SeriesType with get() = this.SeriesType
        member this.Type with get() = this.MatchType
        member this.CompetitionId with get() = this.CompetitionId

    member this.WithFinished finished = { this with Finished = finished}

成员 WithFinished 从 F# 的角度来看非常无用，因为您总是可以直接使用 with 表达式。

let m = { CompetitionID = "1"; Finished = false; ...}
let m2 = { m with CompetitionId = "42" }

但它可能适用于 C# 互操作性。

如果您想将 Match 保留为一个类，那么您应该手动实现 WithFinished 并提供所有参数。

member this.WithFinished finished = 
    Match(competitionId, finished, matchNumber, seriesType, matchType)

但我怀疑它是否有用，因为interfaces在 F# 中始终作为显式实现，这意味着如果不从 F# 端强制转换为 IMatch，您将无法访问 Match 类属性。