Two more questions can be raised about the implementation of extension methods at the level of the compiler. Both those questions relate to the bookkeeping done to mark extension methods and find them during overload resolution.
As with most post-C# 2.0 language features, extension methods are syntactical sugar on top of runtime primitives, introduced to provide more developer convenience. To implement those features, the runtime didn’t have to change at all. This can be seen clearly in the code emitted for our
Reverse extension method call:
var input = Console.ReadLine();Console.WriteLine(input.Reverse());
The preceding code is turned into this:
var input = Console.ReadLine();Console.WriteLine(StringExtensions.Reverse(input)); ...