F# 的标准类型事件是什么？

Question

我正在尝试从 F# 订阅/取消订阅 C# 制作的（在 RabbitMQ 客户端库中）：

AsyncEventingBasicConsumer.cs

public event AsyncEventHandler<BasicDeliverEventArgs> Received;

AsyncEventHandler.cs

public delegate Task AsyncEventHandler<in TEvent>(object sender, TEvent @event) where TEvent : EventArgs;

我成功订阅了活动：

let subscribeAsync (channel: IModel) exchange callback =
    let consumer = AsyncEventingBasicConsumer(channel)
    consumer.add_Received(AsyncEventHandler<BasicDeliverEventArgs>(fun sender args -> Task.CompletedTask))
    // ...

话虽如此，我想知道为什么下面的代码无法编译：

let subscribeAsync (channel: IModel) exchange callback =
    let consumer = AsyncEventingBasicConsumer(channel)
    consumer.Received.AddHandler(AsyncEventHandler<BasicDeliverEventArgs>(fun sender args -> Task.CompletedTask))
    // ...

因为我得到以下错误：

Program.fs(10, 14): [FS1091] The event 'Received' has a non-standard type. If this event is declared in another CLI language, you may need to access this event using the explicit add_Received and remove_Received methods for the event. If this event is declared in F#, make the type of the event an instantiation of either 'IDelegateEvent<_>' or 'IEvent<_,_>'.

我检查了 the official MS documentation 但我看不到任何关于 F# 标准事件类型的参考。

Answer 1

F# 会将 .NET 事件公开为 IEvent 或 IDelegateEvent 类型的值，具体取决于事件声明和委托类型。这只能用于具有一些基本公共结构的事件 - 当 F# 无法执行此操作时，它将公开事件的基础 add 和 remove 操作作为您可以直接调用的方法。

我不确定 "standard event type" 的规则是什么。但是，您可以从 the relevant bit of the F# compiler source code:

得到一些提示

let TryDestStandardDelegateType (infoReader: InfoReader) m ad delTy =
    let g = infoReader.g
    let (SigOfFunctionForDelegate(_, compiledViewOfDelArgTys, delRetTy, _)) =
        GetSigOfFunctionForDelegate infoReader delTy m ad
    match compiledViewOfDelArgTys with 
    | senderTy :: argTys when (isObjTy g senderTy) && 
         not (List.exists (isByrefTy g) argTys)  -> Some(mkRefTupledTy g argTys, delRetTy)
    | _ -> None

所以，我的猜测是 "stadnard event type" 需要：

至少有一个参数
第一个参数的类型必须是object
没有byref个参数

F# 的标准类型事件是什么？

What is a standard type event for F#?

c#

f#

event-handling

rabbitmq

.net-core