如何使用 F# 中的单例模式更新具有记录成员的类

Question

假设我有这个记录定义：

type WindowServices =
    {
        ReportMenu: Window option 
        ProgressNotes: Window option
        PatientRegistration: Window option
    }

此外，我在这个类中尝试实现单例模式：

type WindowServiceManager private(wss) =  
    let mutable ws:WindowServices = wss  
    member this.WS 
        with get () = ws
        and set (value) = ws <- value
    
    static member val Instance = 
            let wss = {ReportMenu = None; ProgressNotes = None; PatientRegistration = None}    
            WindowServiceManager(wss)

在课堂之外，单例“Instance”似乎可以通过以下方式正确获得：

let i = WindowServiceManager.Instance

但是，绝对nothing我试过可以更改默认记录值。也就是说，这失败了。 “windowServices”中的新值永远不会输入到 WS:

let windowServices : WindowServices = 
              { ReportMenu = Some  reportMenu; 
                ProgressNotes = Some progressNoteWindow; 
                PatientRegistration = Some patientRegistrationWindow }
           
i.WS <- windowServices

这是怎么做到的？

TIA

附录：以下显示失败。 “failwith”是总是命中：

let getReportMenuService : Window = 
    let i = WindowServiceManager.Instance
    let p = match i.WS.ReportMenu with
        | None -> failwith "[ReportMenuService] Something went wrong!"
        | Some s -> s
    p

Answer 1

我认为您的代码中还有一些您尚未与我们分享的内容。您提供的代码按预期工作（为简单起见，使用

Window

作为

string

的别名）：

type Window = string

type WindowServices =
    {
        ReportMenu: Window option 
        ProgressNotes: Window option
        PatientRegistration: Window option
    }

type WindowServiceManager private(wss) =  
    let mutable ws:WindowServices = wss  
    member this.WS 
        with get () = ws
        and set (value) = ws <- value
    
    static member val Instance = 
            let wss = {ReportMenu = None; ProgressNotes = None; PatientRegistration = None}    
            WindowServiceManager(wss)

let i = WindowServiceManager.Instance

let windowServices : WindowServices = 
              { ReportMenu = Some "ReportMenu";
                ProgressNotes = Some "ProgressNotes" ;
                PatientRegistration = Some "PatientRegistration" }
           
i.WS <- windowServices

let getReportMenuService : Window = 
    let i = WindowServiceManager.Instance
    let p =
        match i.WS.ReportMenu with
        | None -> failwith "[ReportMenuService] Something went wrong!"
        | Some s -> s
    p

getReportMenuService
    |> printfn "%A"   // "ReportMenu"