How to override generic method with derived type in c#

user_710275 0
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I have the following classes:

public interface IService
{
    void ApplyChanges<T>(T parameters) where T : ParamBase;
}

public class ServiceBase : IService
{
    public virtual void ApplyChanges<T>(T parameters) where T : ParamBase
    { }
}
public abstract class Service : ServiceBase
{
    public override void ApplyChanges<T>(T parameters) where T : ParamBase
    {
        Console.WriteLine(parameters.Param2);
        //Apply changes logic here...
    }
}

public abstract class ParamBase
{
    public string Param1 { get; set; }
}

public class ParamA : ParamBase
{
    public string Param2 { get; set; }
}

Here my test main class:

void Main()
{
  var service = new Service();
  var paramA = new ParamA();
  paramA.Param2 = "Test2";
  service.ApplyChanges<ParamA>(paramA);
}

What is wrong with that implementation? How can I access parameters.Param2from the overriden ApplyChanges method in my Service class?

The general idea is that I have a ServiceBase and I want to be able for its derived classes to pass different parameter types to the ApplyChanges method.

inheritance generics c#
3 Answers

Really, instead of replacing the interface's generic type, it is cleaner to use a "Type Guard". I say cleaner because the interface's method signature stays consistent, and really, what's more important than how your interface is used? (Obviously puppies are more important)

Within the method itself, you can make sure that the type is the one desired as such...

public void Method(ParentRequest req){
if(req is ChildRequest request){
//Do logic here
} else {
    throw new Exception($"request is of type {req.GetType().Name} and must be of type ParentRequest");
    }
}
user_18839610
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