✅ Confusion over defining a default implementation on an interface

I have an interface I'll call

IWidget

IWidget

, and a class which implements it called

Widget

Widget

. I created a property

IWidget

IWidget

with a default implementation. However, I cannot access that property on a

Widget

Widget

instance. My expectation was that any class/interface which implements

IWidget

IWidget

would get its default implementation.

When looking up some of the docs online I see this is expected behavior and has something to do with preventing breaking changes. What I'm not finding is answers to two questions:
- What's the benefit of providing an implementation to begin with if it's not direclty accessable?
- What's the best pattern to follow if there's shared behavior across all implementations of

IWidget

IWidget

? I would assume an extension for

IWidget

IWidget

but would like to confirm

Fuller example:

using System;

namespace Test
{
    public interface IWidget
    {
        public string GetName { get; }
        
        public int GetNumber => 1;    
    }
    
    public class Widget : IWidget
    {
        public string GetName => "Widget";
    }

    public static class Program
    {
        public static void Main(string[] args)
        {
            Widget widget = new Widget();
            IWidget iwidget = widget;

            // both work
            Console.WriteLine(widget.GetName);
            Console.WriteLine(iwidget.GetName);
            
            // widget has an error
            // iwidget works
            Console.WriteLine(widget.GetNumber);
            Console.WriteLine(iwidget.GetNumber);
        }
    }
}

using System;

namespace Test
{
    public interface IWidget
    {
        public string GetName { get; }
        
        public int GetNumber => 1;    
    }
    
    public class Widget : IWidget
    {
        public string GetName => "Widget";
    }

    public static class Program
    {
        public static void Main(string[] args)
        {
            Widget widget = new Widget();
            IWidget iwidget = widget;

            // both work
            Console.WriteLine(widget.GetName);
            Console.WriteLine(iwidget.GetName);
            
            // widget has an error
            // iwidget works
            Console.WriteLine(widget.GetNumber);
            Console.WriteLine(iwidget.GetNumber);
        }
    }
}

✅ Confusion over defining a default implementation on an interface

I have an interface I'll call

IWidget

IWidget

, and a class which implements it called

Widget

Widget

. I created a property

IWidget

IWidget

with a default implementation. However, I cannot access that property on a

Widget

Widget

instance. My expectation was that any class/interface which implements

IWidget

IWidget

IWidget

IWidget

? I would assume an extension for

IWidget

IWidget

but would like to confirm

Fuller example:

using System;

namespace Test
{
    public interface IWidget
    {
        public string GetName { get; }
        
        public int GetNumber => 1;    
    }
    
    public class Widget : IWidget
    {
        public string GetName => "Widget";
    }

    public static class Program
    {
        public static void Main(string[] args)
        {
            Widget widget = new Widget();
            IWidget iwidget = widget;

            // both work
            Console.WriteLine(widget.GetName);
            Console.WriteLine(iwidget.GetName);
            
            // widget has an error
            // iwidget works
            Console.WriteLine(widget.GetNumber);
            Console.WriteLine(iwidget.GetNumber);
        }
    }
}

using System;

namespace Test
{
    public interface IWidget
    {
        public string GetName { get; }
        
        public int GetNumber => 1;    
    }
    
    public class Widget : IWidget
    {
        public string GetName => "Widget";
    }

    public static class Program
    {
        public static void Main(string[] args)
        {
            Widget widget = new Widget();
            IWidget iwidget = widget;

            // both work
            Console.WriteLine(widget.GetName);
            Console.WriteLine(iwidget.GetName);
            
            // widget has an error
            // iwidget works
            Console.WriteLine(widget.GetNumber);
            Console.WriteLine(iwidget.GetNumber);
        }
    }
}

✅ Confusion over defining a default implementation on an interface

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✅ Confusion over defining a default implementation on an interface

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