CODEWITHSUNDEEP
c#generics.net-3.5
Martin
Martin

Reputation: 40573

Generic method with multiple constraints

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

Upvotes: 345

Views: 145163

Answers (4)

LukeH
LukeH

Reputation: 269368

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

Upvotes: 542

Pavel Sem
Pavel Sem

Reputation: 1753

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

Edited as per comment

Upvotes: 7

Hamit YILDIRIM
Hamit YILDIRIM

Reputation: 4539

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

Upvotes: 25

Maytham Fahmi
Maytham Fahmi

Reputation: 33397

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.

Upvotes: 11

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