As far as I know you can’t invoke default interface method implementation in inheriting class (though there were proposals). But you can call it from inheriting interface:
public class HappyGreeter : IGreeter
{
private interface IWorkAround : IGreeter
{
public void SayHello(string name)
{
(this as IGreeter).SayHello(name);
System.Console.WriteLine("I hope you're doing great!!");
}
}
private class WorkAround : IWorkAround {}
public void SayHello(string name)
{
((IWorkAround)new WorkAround()).SayHello(name);
}
}
UPD
In my original answer too much wanted to show that you can call base
in inheriting interface, but as @Alexei Levenkov suggested in comments cleaner way in this particular case would be something like this:
public class HappyGreeter : IGreeter
{
private class WorkAround : IGreeter { }
private static readonly IGreeter _workAround = new WorkAround();
public void SayHello(string name)
{
_workAround.SayHello(name);
System.Console.WriteLine("I hope you're doing great!!");
}
}