没有类型推断与泛型扩展方法 [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;
}

和这个类

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. 在此扩展方法显示在所有类型，甚至字符串。
2. 在我可以不写新EventInvocatorParameters＆LT; EventArgs的＆GT;（EventABC）。直到（E =＆GT;假）; 这是告诉我的方法类型参数。 ..不能从使用的推断。

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."

我不能使用泛型类型参数也是这样吗？你会如何​​解决这个问题？
重要的一点：我需要这两个通用的参数，因为我需要返还相同种类这种扩展方法被称为对

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.

退一步海阔天空（没有必要回答这个问题！）：
我想创建一个流畅的接口调用的事件。该基地是这个静态类：

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;
                }
            }
        }
    }
}

要确保这种方法只能调用完全配置参数，它只接受一个 ConfiguredEventInvocatorParameters＆LT; T＆GT; 这源于 EventInvocatorParameters＆LT; T＆GT ; ：

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; }

}

以下将是有效的电话：

The following would be valid calls:

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));

以下是无效的：

The following would be invalid:

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

，存在一个名为在扩展方法，即接受一个事件处理程序和LT为了使这项工作; TEventArgs 或 TEventInvocatorParameters 并返回 ConfiguredEventInvocatorParameters＆LT; TEventArgs＆GT; 。所有来电继在现在还需要返回值的类型 ConfiguredEventInvocatorParameters＆LT; TEventArgs＆GT; ，一个有效的，否则第二个例子（末尾与到）调用是行不通的。照片 如果在一般的API有什么想法，请让我知道。不过，我想避免以下三件事情：

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:

• 在故障只在运行时，如果参数还没有被完全配置
• 创建像 EventName.With逆语法（...），直到（...）。火灾（）
• 使用臭名昭著的不要方法来开始的事情：火（事件名称）。随着（...）直到（...） 。做（）;

• 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

对于有兴趣的人，现在，我解决了一个通用的类层次结构的原始问题（流利事件调用API）。这基本上是对类固醇Hightechrider的答案。

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);
    }
}

这允许你写code是这样的：

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));

不过，这并不让你写这篇文章，因为不是所有必要的信息（EventArgs的和发件人）已经提供了：

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);

这篇关于没有类型推断与泛型扩展方法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！