C#重载泛型函数

Question

我正在尝试用一个特定的方法重载一个泛型方法。但他不会使用指定类型的方法，他采用的是不会实现的泛型方法。

public static class Functions<TE, TC, TG>
     where TE : Entity, IExternalConexioEntity
     where TC : class, IInternalConexioEntity, IObjectState
     where TG : ConexioEntity
{

public static TG ConvertToEntity(TC conexioEntity)
{
    throw new Exception("Type not supported(" + conexioEntity.GetType() + ")");
}

public static Contact ConvertToEntity(ConexioContact synccontact)
{

}
}

方法调用：

result.Add(ConvertEntity(synchronizationContact));

而且syncrhonizationContact也是一个泛型类型where TC : class, IInternalConexioEntity, IObjectState。所以实际的类型是ConexioContact。

但是他没有运行到第二个方法，我的值是ConexioContact类型的。

Conexio.Data.Entities.Conexio.ConexioContact
System.AggregateException: One or more errors occurred. ---> System.Exception: Type not supported(Conexio.Data.Entities.Conexio.ConexioContact)
   at Conexio.Core.Orchestration.Functions`3.ConvertToEntity(TC conexioEntity) in 
d:\TeamFoundation\Sources\Conexio\Conexio.Core.Orchestration\Functions.cs:line 187
   at Conexio.Core.Orchestration.Contacts.Doubtfuls.SearchDoubtfuls`3.ConvertEntity(TC entity) in d:\TeamFoundation\Sources\Conexio\Conexio.Core.Orchestration\Contacts\Doubtfuls\SearchDoubtfuls.cs:line 107
   at Conexio.Core.Orchestration.Contacts.Doubtfuls.SearchDoubtfuls`3.<SearchAsync>d__5.MoveNext() in d:\TeamFoundation\Sources\Conexio\Conexio.Core.Orchestration\Contacts\Doubtfuls\SearchDoubtfuls.cs:line 61
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at Conexio.Core.Orchestration.Contacts.ConexioEntityBL`3.<SearchDoubtfulsAsync>d__28.MoveNext() in d:\TeamFoundation\Sources\Conexio\Conexio.Core.Orchestration\Contacts\ConexioEntityBL.cs:line 323
   --- End of inner exception stack trace ---
   at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions)
   at System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)
   at System.Threading.Tasks.Task`1.get_Result()
   at Conexio.Core.Orchestration.Test.Doubtfuls.SearchContactsTest.TestSearch4() in d:\TeamFoundation\Sources\Conexio\Conexio.Core.Orchestration.Matching.Test\Doubtfuls\SearchContactsTest.cs:line 90
---> (Inner Exception #0) System.Exception: Type not supported(Conexio.Data.Entities.Conexio.ConexioContact)
   at Conexio.Core.Orchestration.Functions`3.ConvertToEntity(TC conexioEntity) in d:\TeamFoundation\Sources\Conexio\Conexio.Core.Orchestration\Functions.cs:line 187
   at Conexio.Core.Orchestration.Contacts.Doubtfuls.SearchDoubtfuls`3.ConvertEntity(TC entity) in d:\TeamFoundation\Sources\Conexio\Conexio.Core.Orchestration\Contacts\Doubtfuls\SearchDoubtfuls.cs:line 107
   at Conexio.Core.Orchestration.Contacts.Doubtfuls.SearchDoubtfuls`3.<SearchAsync>d__5.MoveNext() in d:\TeamFoundation\Sources\Conexio\Conexio.Core.Orchestration\Contacts\Doubtfuls\SearchDoubtfuls.cs:line 61
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at Conexio.Core.Orchestration.Contacts.ConexioEntityBL`3.<SearchDoubtfulsAsync>d__28.MoveNext() in d:\TeamFoundation\Sources\Conexio\Conexio.Core.Orchestration\Contacts\ConexioEntityBL.cs:line 323<---

Answer 1

你要做的不是重载。它被称为泛型专门化，在C#中不受支持。有一些brittle workarounds只有在编译时知道具体类型时才有效。

如果使用ConexioContact-typed参数进行调用，编译器就会知道第二种方法更具体。

如果你传递一个更泛型的参数，例如IConexioContact或object，编译器会发现它没有特定的方法，但它可以使用泛型方法创建一个。所以ConvertToEntity<IConexioContact>胜过了ConvertToEntity(ConexioContact)，你得到了一个例外。