6

为什么在有区别的联合中不允许使用 let 绑定？我认为这与在默认构造函数中执行的 let 绑定有关吗？

在第二点上，任何关于我如何重写的建议AI_Choose都将不胜感激。我想将加权优先级与 AI 保持在一个元组中。我的想法是AI_Weighted_Priority继承AI_Priority和覆盖选择。我不想处理不同长度的压缩列表（糟糕的做法 imo。）

open AI

type Condition =
    | Closest of float
    | Min
    | Max
    | Average
    member this.Select (aiListWeight : list<AI * float>) =
        match this with
        | Closest(x) -> 
            aiListWeight 
            |> List.minBy (fun (ai, priority) -> abs(x - priority))
        | Min -> aiListWeight |> List.minBy snd
        | Max -> aiListWeight |> List.maxBy snd
        | Average -> 
            let average = aiListWeight |> List.averageBy snd
            aiListWeight 
            |> List.minBy (fun (ai, priority) -> abs(average - priority))

type AI_Choose =
    | AI_Priority of list<AI> * Condition
    | AI_Weighted_Priority of list<AI * float> * Condition

    // I'm sad that I can't do this    
    let mutable chosen = Option<AI>.None

    member this.Choose() =
        match this with
        | AI_Priority(aiList, condition) -> 
            aiList 
            |> List.map (fun ai -> ai, ai.Priority())
            |> condition.Select
            |> fst
        | AI_Weighted_Priority(aiList, condition) -> 
            aiList 
            |> List.map (fun (ai, weight) -> ai, weight * ai.Priority())
            |> condition.Select
            |> fst

    member this.Chosen
        with get() = 
            if Option.isNone chosen then
                chosen <- Some(this.Choose())
            chosen.Value
        and set(x) =
            if Option.isSome chosen then
                chosen.Value.Stop()
            chosen <- Some(x)
            x.Start()

    interface AI with
        member this.Start() =
            this.Chosen.Start()
        member this.Stop() =
            this.Chosen.Stop()
        member this.Reset() =
            this.Chosen <- this.Choose()
        member this.Priority() =
            this.Chosen.Priority()
        member this.Update(gameTime) =
            this.Chosen.Update(gameTime)
4

3 回答 3

3

对于任何感兴趣的人，我最终都派生AI_Priority了AI_Weighted_Priority一个抽象基类。

[<AbstractClass>]
type AI_Choose() =
    let mutable chosen = Option<AI>.None

    abstract member Choose : unit -> AI

    member this.Chosen
        with get() = 
            if Option.isNone chosen then
                chosen <- Some(this.Choose())
            chosen.Value
        and set(x) =
            if Option.isSome chosen then
                chosen.Value.Stop()
            chosen <- Some(x)
            x.Start()

    interface AI with
        member this.Start() =
            this.Chosen.Start()
        member this.Stop() =
            this.Chosen.Stop()
        member this.Reset() =
            this.Chosen <- this.Choose()
        member this.Priority() =
            this.Chosen.Priority()
        member this.Update(gameTime) =
            this.Chosen.Update(gameTime)

type AI_Priority(aiList : list<AI>, condition : Condition) =
    inherit AI_Choose()
    override this.Choose() =
        aiList 
        |> List.map (fun ai -> ai, ai.Priority())
        |> condition.Select
        |> fst

type AI_Weighted_Priority(aiList : list<AI * float>, condition : Condition) =
    inherit AI_Choose()
    override this.Choose() =
        aiList 
        |> List.map (fun (ai, weight) -> ai, weight * ai.Priority())
        |> condition.Select
        |> fst
于 2009-08-26T04:56:14.377 回答
3

重新审视这段代码，我最终接受了 Tomas 的建议，结果变得更加清晰。

type AiChooseOptions =
    | Priority of List<AI * Priority>
    | WeightedPriority of List<AI * Priority * float>
    member this.Choose(condition : Condition) =
        match this with
        | Priority(list) ->
            list 
            |> List.map (fun (ai, priority) -> ai, priority.Priority())
            |> condition.Select
        | WeightedPriority(list) ->
            list 
            |> List.map (fun (ai, p, weight) -> ai, p.Priority() * weight)
            |> condition.Select

type AiChoose(condition, list : AiChooseOptions ) =
    let mutable chosen = Unchecked.defaultof<AI>, 0.0

    interface AI with
        member this.Update(gameTime) =
            (fst chosen).Update(gameTime)

    interface Priority with
        member this.Priority() =
            chosen <- list.Choose(condition)
            (snd chosen)
于 2009-10-06T04:35:42.983 回答
2

允许在有区别的工会内进行“让”绑定是有意义的。我认为不可能的原因是可区分联合仍然基于 OCaml 设计，而对象来自 .NET 世界。F# 正在尝试尽可能多地集成这两者，但它可能会走得更远。

无论如何，在我看来，您使用歧视联合只是为了实现该AI_Choose类型的一些内部行为。在这种情况下，您可以单独声明一个可区分联合并使用它来实现对象类型。

我相信你可以这样写：

type AiChooseOptions =
    | AI_Priority of list<AI> * Condition
    | AI_Weighted_Priority of list<AI * float> * Condition

type AiChoose(aiOptions) = 
    let mutable chosen = Option<AI>.None
    member this.Choose() =
        match aiOptions with
        | AI_Priority(aiList, condition) -> (...)
        | AI_Weighted_Priority(aiList, condition) -> (...)
    member this.Chosen (...)
    interface AI with (...)

类层次结构和有区别的联合之间的主要区别在于可扩展性。类使添加新类型变得更容易，而区分联合使添加与类型一起使用的新函数变得更容易（在您的情况下为 AiChooseOptions），因此这可能是设计应用程序时首先要考虑的事情。

于 2009-08-26T23:31:12.907 回答