Question

Is it possible to define an interface (e.g. MyClass Implements MyInterface) whose method/property definitions already match some of the methods/properties defined on a third-party (or a native) class?

For example, the DataRow class has a number of properties/methods that make it “row-like”. What if I want to implement an interface (i.e. IRowLike) that defines certain methods and properties already existing on the native DataRow class (which I cannot directly touch or extend). I simply want the class to agree at runtime that it does indeed abide by some interface.

Interfaces afford a poor-man’s version of “duck typing”. Once I have a set of classes that all abide by a given interface, I can define extension methods against that interface and all classes that support the interface immediately gain new behavior. I know it may seem odd to want to retroactively apply an interface against third-party classes, but it would definitely allows us to do more with less code.

Answer 1

This isn’t possible in .Net. A type defines the interfaces that it implements in metadata at compile time and its definition isn’t alterable at runtime. It is possible to generate types at runtime which implement specific interfaces but not alter an existing type

There are some alternatives though. In VB.Net you could simply choose to use late binding on the type and access the interface methods in that manner (or dynamic in C#) The downside of course is the code isn’t statically verifiable.