没有通用扩展方法的类型推断 [英] No type inference with generic extension method

问题描述

我有以下方法:

public static TEventInvocatorParameters Until
    <TEventInvocatorParameters, TEventArgs>(this TEventInvocatorParameters p,
                                            Func<TEventArgs, bool> breakCond)
    where TEventInvocatorParameters : EventInvocatorParameters<TEventArgs>
    where TEventArgs : EventArgs
{
    p.BreakCondition = breakCond;
    return p;
}

还有这个班

public class EventInvocatorParameters<T>
    where T : EventArgs
{
    public Func<T, bool> BreakCondition { get; set; }
    // Other properties used below omitted for brevity.
}

现在，我有以下问题:

1. 此扩展方法显示在所有类型上，甚至是 string.
2. 我不能写 new EventInvocatorParameters(EventABC).Until(e => false); 它告诉我方法的类型参数......不能从用法."

1. This extension method shows on all types, even string.
2. I can't write new EventInvocatorParameters<EventArgs>(EventABC).Until(e => false); It is telling me "The type arguments for method ... cannot be inferred from the usage."

我不能像这样使用泛型类型参数吗?你会如何解决这个问题?
重点:我需要这两个泛型参数，因为我需要返回调用此扩展方法的相同类型.

Can't I use generic type parameters like this? How would you resolve this problem?
Important point: I need both of those generic parameters, because I need to return the same type this extension method was called on.

大图(回答问题不需要！):
我正在尝试创建一个流畅的界面来调用事件.基础是这个静态类:

Broader picture (not necessary for answering the question!):
I am trying to create a fluent interface to invoking events. The base is this static class:

public static class Fire
{
   public static void Event<TEventArgs>(
       ConfiguredEventInvocatorParameters<TEventArgs> parameters)
    where TEventArgs : EventArgs
    {
        if (parameters.EventHandler == null)
        {
            return;
        }

        var sender = parameters.Sender;
        var eventArgs = parameters.EventArgs;
        var breakCondition = parameters.BreakCondition;

        foreach (EventHandler<TEventArgs> @delegate in 
                 parameters.EventHandler.GetInvocationList())
        {
            try
            {
                @delegate(sender, eventArgs);
                if (breakCondition(eventArgs))
                {
                    break;
                }
            }
            catch (Exception e)
            {
                var exceptionHandler = parameters.ExceptionHandler;
                if (!exceptionHandler(e))
                {
                    throw;
                }
            }
        }
    }
}

为了确保只能使用完全配置的参数调用此方法，它只接受从 EventInvocatorParameters 派生的 ConfiguredEventInvocatorParameters:

To make sure this method can only be called with fully configured parameters, it only accepts a ConfiguredEventInvocatorParameters<T> which derives from EventInvocatorParameters<T>:

public class ConfiguredEventInvocatorParameters<T>
    : EventInvocatorParameters<T>
    where T : EventArgs
{
    public ConfiguredEventInvocatorParameters(
        EventInvocatorParameters<T> parameters, object sender, T eventArgs)
        : base(parameters)
    {
        EventArgs = eventArgs;
        Sender = sender;
    }

    public T EventArgs { get; private set; }
    public object Sender { get; private set; }

}

以下是有效的调用:

Fire.Event(EventName.With(sender, eventArgs));
Fire.Event(EventName.With(sender, eventArgs).Until(e => e.Cancel));
Fire.Event(EventName.Until(e => e.Cancel).With(sender, eventArgs));

以下内容无效:

// no sender or eventArgs have been specified, i.e. missing call to With(...)
Fire.Event(EventName.Until(e => e.Cancel));

为了完成这项工作，存在名为 With 的扩展方法，它们接受 EventHandler 或 TEventInvocatorParameters 并返回一个 <代码>ConfiguredEventInvocatorParameters.With 之后的所有调用现在还需要返回类型 ConfiguredEventInvocatorParameters，否则有效调用的第二个示例(带有 Until最后)不起作用.
如果您对 API 有任何想法，请告诉我.但是，我想避免以下三件事:

To make this work, there exist extension methods named With, that accept either a EventHandler<TEventArgs or a TEventInvocatorParameters and return a ConfiguredEventInvocatorParameters<TEventArgs>. All calls following the With now also need to return the type ConfiguredEventInvocatorParameters<TEventArgs>, otherwise the second example of a valid call (with the Until at the end) wouldn't work.
If you have any thoughts on the API in general, please let me know. However, I want to avoid the following three things:

• 仅在参数未完全配置时才会在运行时失败
• 创建类似 EventName.With(...).Until(...).Fire() 的反向语法
• 使用臭名昭著的 Do 方法开始:Fire(EventName).With(...).Until(...).Do();

• Fail only at runtime if the parameters have not been configured fully
• Creating an inverse syntax like EventName.With(...).Until(...).Fire()
• Use the infamous Do method to start off things: Fire(EventName).With(...).Until(...).Do();

推荐答案

对于任何感兴趣的人，现在，我使用通用类层次结构解决了原始问题(流畅的事件调用 API).这基本上是 Hightechrider 对类固醇的回答.

For anyone interested, for now, I solved the original problem (fluent event invocation API) with a generic class hierarchy. This is basically Hightechrider's answer on steroids.

public abstract class EventInvocatorParametersBase
    <TEventInvocatorParameters, TEventArgs>
    where TEventArgs : EventArgs
    where TEventInvocatorParameters :
        EventInvocatorParametersBase<TEventInvocatorParameters, TEventArgs>

{
    protected EventInvocatorParametersBase(
        EventHandler<TEventArgs> eventHandler,
        Func<Exception, bool> exceptionHandler,
        Func<TEventArgs, bool> breakCondition)
    {
        EventHandler = eventHandler;
        ExceptionHandler = exceptionHandler;
        BreakCondition = breakCondition;
    }

    protected EventInvocatorParametersBase(
        EventHandler<TEventArgs> eventHandler)
        : this(eventHandler, e => false, e => false)
    {
    }

    public Func<TEventArgs, bool> BreakCondition { get; set; }
    public EventHandler<TEventArgs> EventHandler { get; set; }
    public Func<Exception, bool> ExceptionHandler { get; set; }

    public TEventInvocatorParameters Until(
        Func<TEventArgs, bool> breakCondition)
    {
        BreakCondition = breakCondition;
        return (TEventInvocatorParameters)this;
    }

    public TEventInvocatorParameters WithExceptionHandler(
        Func<Exception, bool> exceptionHandler)
    {
        ExceptionHandler = exceptionHandler;
        return (TEventInvocatorParameters)this;
    }

    public ConfiguredEventInvocatorParameters<TEventArgs> With(
        object sender, 
        TEventArgs eventArgs)
    {
        return new ConfiguredEventInvocatorParameters<TEventArgs>(
            EventHandler, ExceptionHandler, BreakCondition,
            sender, eventArgs);
    }
}

public class EventInvocatorParameters<T> :
    EventInvocatorParametersBase<EventInvocatorParameters<T>, T>
    where T : EventArgs
{
    public EventInvocatorParameters(EventHandler<T> eventHandler)
        : base(eventHandler)
    {
    }
}

public class ConfiguredEventInvocatorParameters<T> :
    EventInvocatorParametersBase<ConfiguredEventInvocatorParameters<T>, T>
    where T : EventArgs
{
    public ConfiguredEventInvocatorParameters(
        EventHandler<T> eventHandler,
        Func<Exception, bool> exceptionHandler,
        Func<T, bool> breakCondition, object sender,
        T eventArgs)
        : base(eventHandler, exceptionHandler, breakCondition)
    {
        EventArgs = eventArgs;
        Sender = sender;
    }

    public ConfiguredEventInvocatorParameters(EventHandler<T> eventHandler,
                                              object sender,
                                              T eventArgs)
        : this(eventHandler, e => false, e => false, sender, eventArgs)
    {
    }

    public T EventArgs { get; private set; }
    public object Sender { get; private set; }
}

public static class EventExtensions
{
    public static EventInvocatorParameters<TEventArgs> Until<TEventArgs>(
        this EventHandler<TEventArgs> eventHandler,
        Func<TEventArgs, bool> breakCondition)
        where TEventArgs : EventArgs
    {
        return new EventInvocatorParameters<TEventArgs>(eventHandler).
            Until(breakCondition);
    }

    public static EventInvocatorParameters<TEventArgs> 
        WithExceptionHandler<TEventArgs>(
            this EventHandler<TEventArgs> eventHandler,
            Func<Exception, bool> exceptionHandler)
        where TEventArgs : EventArgs
    {
        return
            new EventInvocatorParameters<TEventArgs>(eventHandler).
                WithExceptionHandler(exceptionHandler);
    }

    public static ConfiguredEventInvocatorParameters<TEventArgs>
        With<TEventArgs>(
            this EventHandler<TEventArgs> eventHandler, object sender,
            TEventArgs eventArgs)
        where TEventArgs : EventArgs
    {
        return new ConfiguredEventInvocatorParameters<TEventArgs>(
            eventHandler, sender, eventArgs);
    }
}

这允许您编写这样的代码:

This allows you to write code like this:

Fire.Event(EventName.WithExceptionHandler(e => false)
                    .Until(e => false).With(this, EventArgs.Empty));
Fire.Event(EventName.With(this, EventArgs.Empty));
Fire.Event(EventName.WithExceptionHandler(e => false)
                    .With(this, EventArgs.Empty).Until(e => false));
Fire.Event(EventName.With(this, EventArgs.Empty)
                    .WithExceptionHandler(e => false).Until(e => false));

但它不允许你写这个，因为没有提供所有必要的信息(eventArgs和sender):

But it doesn't allow you to write this, because not all necessary info (eventArgs and sender) has been provided:

Fire.Event(EventName.Until(e => false));
Fire.Event(EventName);

这篇关于没有通用扩展方法的类型推断的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！