How do extension methods work under-the-hood?

Question

A contractor where I work is using extension methods to implement CRUD on well-known internal classes that we own. I say it is better

Answer 1

How do extension methods work under-the-hood?

They're just static methods; the compiler rewrites calls like myObject.MyExtensionMethod() to MyExtensionClass.MyExtensionMethod(myObject).

Is it better to use inheretance or extension methods on WELL-KNOWN classes that you OWN?

There's not single answer to this question, it all depends on the context. But usually extension methods are most useful in those cases:

• you don't own the code for the extended type
• the method targets an interface and will be the same for all implementations of this interface (e.g. IEnumerable and Linq extension methods)