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F# 中全局变量的样式指南

发布于 2024-11-07 22:31:14 字数 258 浏览 0 评论 0原文

我需要一个全局变量（我可以构建它，然后将其传递给每个函数调用，并让每个函数调用都知道它，但这似乎很老套，可读性较差，工作量也更大）。全局变量是游戏的查找表（残局：开局书和换位/缓存）。

某些代码可能会失去其幂等行为，这实际上是重点（加速）。我知道全局可变状态很糟糕，但这是值得的（10 倍以上的性能提升）。那么如何构建单例或在具有组合器的静态类中使用静态值呢？

它们实际上是相同的，但我很好奇人们在这类问题上做了什么。或者我应该把这个东西传递给每个人（或者至少是一个参考）？

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醉生梦死 2024-11-14 22:31:14

这是一个类似于@Yin Zhu 发布的解决方案，但使用抽象类型来指定可变值的使用接口，使用本地定义来封装它，并使用对象文字来提供实现（这取自 Expert F#--由唐·赛姆 (Don Syme) 合着）：

type IPeekPoke =
    abstract member Peek: unit -> int
    abstract member Poke: int -> unit

let makeCounter initialState =
    let state = ref initialState
    { new IPeekPoke with
        member x.Poke(n) = state := !state + n
        member x.Peek() = !state }

Here is a solution similar to the one posted by @Yin Zhu's, but using abstract types to specify a usage interface for the mutable value, a local definition to encapsulate it and object literals to provide an implementation (this is taken from Expert F#--which is co-authored by Don Syme):

type IPeekPoke =
    abstract member Peek: unit -> int
    abstract member Poke: int -> unit

let makeCounter initialState =
    let state = ref initialState
    { new IPeekPoke with
        member x.Poke(n) = state := !state + n
        member x.Peek() = !state }

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小糖芽 2024-11-14 22:31:14

您还可以使用静态字段来完成此操作，如下所示：

type Common() = 

    static let mutable queue : CloudQueue = null
    static let mutable storageAccount : CloudStorageAccount = null

    static member Queue 
        with get() = queue
        and set v = queue <- v
    static member StorageAccount 
        with get() = storageAccount
        and set v = storageAccount <- v

在另一个模块中，只需：

open Common
Common.Queue <- xxxx

You can also do it with static fields, like this:

type Common() = 

    static let mutable queue : CloudQueue = null
    static let mutable storageAccount : CloudStorageAccount = null

    static member Queue 
        with get() = queue
        and set v = queue <- v
    static member StorageAccount 
        with get() = storageAccount
        and set v = storageAccount <- v

In another module, just:

open Common
Common.Queue <- xxxx

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泪眸﹌ 2024-11-14 22:31:14

以下是 F# PowerPack Matrix 库 (\src\FSharp.PowerPackmath\associations.fs) 中使用的约定：

// put global variable in a special module
module GlobalAssociations =
    // global variable ht
    let ht = 
        let ht = new System.Collections.Generic.Dictionary<Type,obj>() 
        let optab =
            [ typeof<float>,   (Some(FloatNumerics    :> INumeric<float>) :> obj);
              typeof<int32>,   (Some(Int32Numerics    :> INumeric<int32>) :> obj);
                  ...
              typeof<bignum>,  (Some(BigRationalNumerics   :> INumeric<bignum>) :> obj); ]

        List.iter (fun (ty,ops) -> ht.Add(ty,ops)) optab;
        ht

    // method to update ht
    let Put (ty: System.Type, d : obj)  =
        // lock it before changing
        lock ht (fun () -> 
            if ht.ContainsKey(ty) then invalidArg "ty" ("the type "+ty.Name+" already has a registered numeric association");
            ht.Add(ty, d))

here is the convention used in F# PowerPack Matrix library (\src\FSharp.PowerPackmath\associations.fs):

// put global variable in a special module
module GlobalAssociations =
    // global variable ht
    let ht = 
        let ht = new System.Collections.Generic.Dictionary<Type,obj>() 
        let optab =
            [ typeof<float>,   (Some(FloatNumerics    :> INumeric<float>) :> obj);
              typeof<int32>,   (Some(Int32Numerics    :> INumeric<int32>) :> obj);
                  ...
              typeof<bignum>,  (Some(BigRationalNumerics   :> INumeric<bignum>) :> obj); ]

        List.iter (fun (ty,ops) -> ht.Add(ty,ops)) optab;
        ht

    // method to update ht
    let Put (ty: System.Type, d : obj)  =
        // lock it before changing
        lock ht (fun () -> 
            if ht.ContainsKey(ty) then invalidArg "ty" ("the type "+ty.Name+" already has a registered numeric association");
            ht.Add(ty, d))

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