Interface 在F#中，如何在lambda表达式中转换接口？

我发现F#中的接口概念与C#有很大的不同

但是，在实现以下接口时：

type IVisit = 
    abstract member lastname: string with get
    abstract member firstname: string with get
    abstract member mi: string with get
    abstract member birthdate: Nullable<DateTime> with get
    abstract member appointmentTime : System.Nullable<DateTime> with get
    abstract member tservice : System.Nullable<DateTime> with get
    abstract member postingTime : System.Nullable<DateTime> with get
    abstract member chartNumber : System.Nullable<int> with get

type Visit = 
    interface IVisit with 
        member this.lastname = "lastname"
        member this.firstname = "FirstName"
        member this.mi = "mi"
        member this.birthdate = Nullable(DateTime(2020, 1, 1))
        member this.appointmentTime = Nullable(DateTime(2020, 1, 1)) 
        member this.tservice = Nullable(DateTime(2020, 1, 1)) 
        member this.postingTime = Nullable(DateTime(2020, 1, 1)) 
        member this.chartNumber = Nullable(0)

正在尝试使用Visit:>IVisit.lastname=…，或Visit:#IVisit.lastname=…，强制转换“Visit”。。。也失败了。我相信这很简单，这是怎么做到的

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谢谢您的帮助。

您在第二个代码段中使用的语法是用于记录初始化的代码段。但是，您希望创建接口的实例

您可以通过创建一个类来实现这一点，但是您的类定义还没有完全实现，因为它没有构造函数。所以，你需要一些大致的东西：

type Visit(first:string, last:string) = 
  interface IVisit with
    member x.first = first
    member x.last = last

这会变得相当麻烦，所以我会使用另一个F#特性，匿名对象表达式，它允许您创建一个没有类的接口实例：

 { new IVisit with 
    member x.first = "Yadda"
    member x.last = "Yadda" }

使用此选项，您的代码将如下所示：

let context = Wsdl1.GetBasicHttpBinding_IMedicalService()
let GetScheduleAsync (tableDate : DateTime) =
    async {
        let data = context.GetOfficeScheduleAsync(tableDate) |> Async.AwaitTask
        return data |> Seq.map(fun q -> 
          { new IVisit with 
            member this.mi = "??"
            member this.lastname = q.lastname
            member this.firstname = q.firstname
            member this.birthdate = q.birthdate
            member this.appointmentTime = q.appointment_time
            member this.tservice = q.service_time
            member this.postingTime = q.posting_time
            member this.chartNumber = q.chart_number })                  
    }
   |> Async.StartAsTask

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也就是说，我真的不明白为什么这里需要一个接口，而不是普通的F#record。即使要从C#使用此库，记录看起来也会像普通类。

要使用接口创建值，必须使用对象表达式语法，或实现类（），您所做的是尝试创建类型为“Visit”的记录，而不是记录。我的C#代码使用接口作为DI，例如List（）。我的想法是，要在C#中统计List（），F#记录必须实现IVisit。我错了吗？谢谢。@AlanWayne是的，没错-但是我不明白为什么对于一个简单的记录类型需要依赖注入。记录只是存储数据，它是由编译器生成的，因此它是正确的，我怀疑您是否会想用另一个实现来替换它……在C代码中，我有多个不同的记录类型，它们有更多的字段，然后用IVisit表示。然而，我的一些方法只依赖于IVisit中的字段。因此，允许不同类型共享公共IVisit接口，我可以将相同的方法应用于不同的结构。在这两种情况下，我是否可以使用匿名对象来统计C#List？或者你建议怎么做？谢谢。@AlanWayne您可以在另一条记录中放入

Visit

：

键入SomeType={FirstVisit:Visit；OtherInfo:OtherInfo}

。仅仅对数据进行分组，接口就显得非常重要。

 { new IVisit with 
    member x.first = "Yadda"
    member x.last = "Yadda" }

let context = Wsdl1.GetBasicHttpBinding_IMedicalService()
let GetScheduleAsync (tableDate : DateTime) =
    async {
        let data = context.GetOfficeScheduleAsync(tableDate) |> Async.AwaitTask
        return data |> Seq.map(fun q -> 
          { new IVisit with 
            member this.mi = "??"
            member this.lastname = q.lastname
            member this.firstname = q.firstname
            member this.birthdate = q.birthdate
            member this.appointmentTime = q.appointment_time
            member this.tservice = q.service_time
            member this.postingTime = q.posting_time
            member this.chartNumber = q.chart_number })                  
    }
   |> Async.StartAsTask