public interface IInterface1 {};
public interface IEtcetera {};
 
public struct CanUseThis : IEtcetera, IInterface1 {}
public class  OrThat     : IEtcetera, IInterface1 {}
 
public class Foo
{
    private IInterface1 _object; // just pick one
 
    public void setObject<T>(T obj)
        where T : IInterface1, IEtcetera
    {
        // you now *know* that object supports all the interfaces
        // you don't need the compiler to remind you
        _object = obj; 
    }
 
    public void ExerciseObject()
    { 
        // completely safe due to the constraints on setObject<T>
        IEtcetera itf = (IEtcetera) _object;
 
        // ....
    }
}
 
public class Program
{
    public static void Main(string[] args)
    {
        var foo = new Foo();
 
        foo.setObject(new CanUseThis());
        foo.ExerciseObject();
 
        foo.setObject(new OrThat());
        foo.ExerciseObject();
    }
}
 

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