Markup Interface

Question

What is the markup interface in C#? is Microsoft really implement inside FCL Or BCL? if yes then where?

Vulpes · Accepted Answer

Yes, it looks like there might a few of these in the .NET Framework.
I've found another one here:
http://msdn.microsoft.com/en-us/library/system.web.ui.inamingcontainer.aspx
Curiously, the use of marker interfaces is contrary to Microsoft's own guidelines for interface design!
http://msdn.microsoft.com/en-us/library/ms229022.aspx

Amit Patel · Answer

Hey Vuples,
You are correct. Markup interface dose not contains any members. Microsoft is also using this concept inside the FCL Or BCL.
See that link.
http://msdn.microsoft.com/en-us/library/system.web.sessionstate.irequiressessionstate.aspx

Vulpes · Answer

I've never heard of a markup interface in relation to C# or .NET but there is something called a 'marker' interface which is simply an interface which has no members.
These can be useful when used in conjunction with extension methods.
A class which implements the marker interface doesn't have to implement any methods but, in effect, methods can be added to the class as extension methods.  These methods will extend any class which is 'marked' as implementing the interface.