Why can't these type parameters be output?

Question

Given the following interfaces / classes:

public interface IRequest<TResponse> { }

public interface IHandler<TRequest, TResponse>
    where TRequest : IRequest<TResponse>
{
    TResponse Handle(TRequest request);
}

public class HandlingService
{
    public TResponse Handle<TRequest, TResponse>(TRequest request)
        where TRequest : IRequest<TResponse>
    {
        var handler = container.GetInstance<IHandler<TRequest, TResponse>>();
        return handler.Handle(request);
    }
}

public class CustomerResponse
{
    public Customer Customer { get; set; }
}

public class GetCustomerByIdRequest : IRequest<CustomerResponse>
{
    public int CustomerId { get; set; }
}

Why the compiler cannot infer the correct types if I try to write something like the following:

var service = new HandlingService();
var request = new GetCustomerByIdRequest { CustomerId = 1234 };
var response = service.Handle(request);  // Shouldn't this know that response is going to be CustomerResponse?

I just get the message "type arguments cannot be deduced." Is this a limitation with the general type of output in general, or is there a way to make this work?

Answer 1

TRequest : IRequest<TResponse>, , TResponse TRequest. , , TRequest IRequest<TResponse>; , , , , .

, Handle (TRequest TResponse), , . Inferrence , , .

Answer 2

, ...

- ( ) service.Handle();

, , .

... ( )

public class MyClass
{
     var service = new HandlingService();
     var request = new GetCustomerByIdRequest { CustomerId = 1234 };
     var response = service.Handle(request);
}

... ( , TResponse)

public class MyClass<TResponse> where TResponse : YOURTYPE
{
     var service = new HandlingService();
     var request = new GetCustomerByIdRequest { CustomerId = 1234 };
     var response = service.Handle(request);
}