Generic method with multiple constraints

Question

I have a generic method which has two generic parameters. I tried to compile the code below but it doesn't work. Is it a .NET limitation? Is it possible to have multiple constraints for different parameter?

public TResponse Call<TResponse, TRequest>(TRequest request)
  where TRequest : MyClass, TResponse : MyOtherClass

Answer 1

It is possible to do this, you've just got the syntax slightly wrong. You need a where for each constraint rather than separating them with a comma:

public TResponse Call<TResponse, TRequest>(TRequest request)
    where TRequest : MyClass
    where TResponse : MyOtherClass

Answer 2

In addition to the main answer by @LukeH with another usage, we can use multiple interfaces instead of class. (One class and n count interfaces) like this

public TResponse Call<TResponse, TRequest>(TRequest request)
  where TRequest : MyClass, IMyOtherClass, IMyAnotherClass

or

public TResponse Call<TResponse, TRequest>(TRequest request)
  where TRequest : IMyClass,IMyOtherClass

Answer 3

In addition to the main answer by @LukeH, I have issue with dependency injection, and it took me some time to fix this. It is worth to share, for those who face the same issue:

public interface IBaseSupervisor<TEntity, TViewModel> 
    where TEntity : class
    where TViewModel : class

It is solved this way. in containers/services the key is typeof and the comma (,)

services.AddScoped(typeof(IBaseSupervisor<,>), typeof(BaseSupervisor<,>));

This was mentioned in this answer.

Answer 4

Each constraint need to be on own line and if there are more of them for single generic parameter then they need to separated by comma.

public TResponse Call<TResponse, TRequest>(TRequest request)
    where TRequest : MyClass, 
    where TResponse : MyOtherClass, IOtherClass