C＃5.0泛型：參數類型推斷

我一直下的印象是，C＃編譯器能夠推斷類型PARAMS的情況下，像以下：爲什麼這C＃5.0泛型：參數類型推斷

class Program 
{ 
    static void Main(string[] args) 
    { 
     IMessageBus messageBus = null; 

     //Here the compiler nags "type params for Publish cannot be inferred from the usage.. .." 
     messageBus.Publish(new CorrectorAdded(10)); 
    } 
} 

public interface IEvent<out TPayload> 
{ 
    TPayload Payload { get; } 
} 

public abstract class EventBase<TPayload> : IEvent<TPayload> 
{ 
    public TPayload Payload { get; private set; } 

    protected EventBase(TPayload payload) 
    { 
     Payload = payload; 
    } 
} 

public interface IMessageBus 
{ 
    void Publish<TEvent, TPayload>(TEvent @event) where TEvent : IEvent<TPayload>; 

    IDisposable Subscribe<TEvent, TPayload>(Action<TPayload> listener) where TEvent : IEvent<TPayload>; 
} 

public class CorrectorAdded : EventBase<CorrectorAddedArgs> 
{ 
    public CorrectorAdded(CorrectorAddedArgs payload) : base(payload) 
    { 
    } 

    public CorrectorAdded(int correctorId) : this(new CorrectorAddedArgs(correctorId)) 
    { 
    } 
} 

public class CorrectorAddedArgs 
{ 
    public int CorrectorId { get; private set; } 

    public CorrectorAddedArgs(int correctorId) 
    { 
     CorrectorId = correctorId; 
    } 
}

任何想法正在發生的事情，以及如何在這種情況下得到類型推理工作？

謝謝。

來源

2013-11-09 Ant

可能重複http://stackoverflow.com/questions/6630690/wh y-cant-nested-generic-types-beferred（不是完全相同的問題，但Eric Lippert的答案也適用於你的問題）。 – haim770

爲publish接口簽名定義2層的約束：

void Publish<TEvent, TPayload>(TEvent @event) where TEvent : IEvent<TPayload>;

TEvent這將是該方法參數簽名
TPayload其中指出TEvent必須實現的接口IEvent<TPayload>

如果發佈方法只有的約束，則編譯器可以推斷的使用，因爲已經定義了類型約束的方法的簽名，即，

void Publish<TEvent>(TEvent @event);

上面然後將允許方法調用，而不類型約束將被使用，即，

messageBus.Publish(new CorrectorAdded(10)); 
// would be the same as 
messageBus.Publish<CorrectorAdded>(new CorrectorAdded(10));

然而，由於接口定義了第二個限制，編譯器不知道的意圖是什麼TPayload，因爲事件可以實現任意數量的IEvent<TPayload>的。但是，如果方法簽名的確包括TPayload類型，則編譯器可能實際推斷約束，即

void Publish<TEvent, TPayload>(TEvent @event, TPayload payload) where TEvent : IEvent<TPayload>;

然後再方法可以在沒有類型約束調用：

messageBus.Publish(new CorrectorAdded(10), new FooThatImplementsTPayload());

來源

2013-11-09 20:29:42

謝謝！這清除了一切。沒有讓我的生活變得更輕鬆，但是由於API看起來很模糊=）。將需要扭轉周圍也許.. .. – Ant

要那些誰仍然好奇如何替代API可能看起來像，這裏是我想出了：

class Program 
{ 
    static void Main(string[] args) 
    { 
     IMessageBus messageBus = null; 

     messageBus 
      .Event<CorrectorAdded>() 
      .Subscribe(eventArgs => { /*skipped*/ }); 

     //skipped 

     messageBus 
      .Event<CorrectorAdded>() 
      .Publish(new CorrectorAddedArgs(1)); 
    } 
} 

public abstract class EventBase 
{ 
    //skipped 
} 

public abstract class EventBase<TPayload> : EventBase 
{ 
    public IDisposable Subscribe(Action<TPayload> listener) 
    { 
     //skipped 
    } 

    public void Publish(TPayload payload) 
    { 
     //skipped 
    } 
} 

public class CorrectorAdded : EventBase<CorrectorAddedArgs> 
{ 
} 

public class CorrectorAddedArgs 
{ 
    public int CorrectorId { get; private set; } 

    public CorrectorAddedArgs(int correctorId) 
    { 
     CorrectorId = correctorId; 
    } 
} 

public interface IMessageBus 
{ 
    TEvent Event<TEvent>() where TEvent : EventBase, new(); 
}

來源

2013-11-10 10:11:05 Ant

C＃5.0泛型：參數類型推斷

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