Struct F#可变值是不可变的

我有下面的结构，它应该允许我创建，然后修改时间和值属性，这将更改私有可变值x.time和x.value

type TimeDataPoint = 
    struct
        val mutable private Time_: DateTime
        val mutable private Value_: double

        new (time: DateTime, value: double) = 
            {
                Time_ = time
                Value_ = value
            }

        member public x.Time
            with get() = x.Time_
            and set(time: DateTime) = x.Time_ <- time

        member public x.Value
            with get() = x.Value_
            and set(value: double) = x.Value_ <- value

    end

---

我该如何解决这个问题？

您还需要将您的

tdp

标记为可变。精简代码如下所示，并输出：

Ticks is 0
Ticks is 636028131920527873

正如所料

module Mutation
open System
type TimeDataPoint = 
    struct
        val mutable private Time_: DateTime
        new (time: DateTime) = 
            {
                Time_ = time
            }
        member public x.Time
            with get() = x.Time_
            and set(time: DateTime) = x.Time_ <- time
    end

let usingTdp() = 
    let mutable tdp = TimeDataPoint()
    printfn "Ticks is %i" tdp.Time.Ticks
    tdp.Time <- DateTime.Now
    printfn "Ticks is %i" tdp.Time.Ticks

如果你和F一起工作，你可能会考虑重新思考变异是否真的是你唯一的选择——我怀疑是。

PS：如果您决定使用一个突变对象，请考虑使用Auto属性语法，它允许您将类定义缩短为：

type TimeDataPoint(v, d) = 
    member val Value: int = v with get, set
    member val Time: DateTime = d with get, set

---

只要我将

tdp

定义为

let mutable tdp=TimeDataPoint（）

，就可以很好地工作。你能发布更多的内容吗？你最好的选择是不要走这条路。NET struct设计指南建议您最好避免可变值类型：您要求通过使可变结构变得有意义而进入一个混乱的世界。我将结构更改为常规类。谢谢。您能发布问题的完整副本吗？

TimeDataPoint

中存储的变量只有在

TimeDataPoint

为结构时才需要可变。如果它是一个类，那么该变量将保存对该类实例的引用，并且在修改该类的属性时，该引用不需要更改。对于没有引用的结构，数据存储在变量中，因此修改结构意味着修改变量，这就是为什么变量本身需要是可变的。

module Mutation
open System
type TimeDataPoint = 
    struct
        val mutable private Time_: DateTime
        new (time: DateTime) = 
            {
                Time_ = time
            }
        member public x.Time
            with get() = x.Time_
            and set(time: DateTime) = x.Time_ <- time
    end

let usingTdp() = 
    let mutable tdp = TimeDataPoint()
    printfn "Ticks is %i" tdp.Time.Ticks
    tdp.Time <- DateTime.Now
    printfn "Ticks is %i" tdp.Time.Ticks

type TimeDataPoint = 
    val mutable private _v: int
    new (v: int) = 
        {
            _v = v
        }
    member public this.Value
        with get() = this._v
        and set(v: int) = this._v <- v

let myList = LinkedList<TimeDataPoint>()
myList.AddFirst(TimeDataPoint(1)) |> ignore
myList.First.Value.Value <- 1

type TimeDataPoint(v, d) = 
    member val Value: int = v with get, set
    member val Time: DateTime = d with get, set