C# 5.0 Unleashed

Building Awaitable Types

Starting from C# 3.0, new language features have not required any change to the underlying CLR infrastructure. This is no different for the asynchronous programming features introduced in C# 5.0. As discussed in depth in the previous section, asynchronous methods use a crafty compile-time rewrite technique to produce a regular method from the runtime’s point of view. Control flow constructs are rewritten in terms of interactions with a method builder object provided in the BCL for .NET Framework 4.5.

Although you could totally imagine a runtime extension to make methods pausable—effectively hoisting the stack frame onto the heap, or using a different technique altogether—there’s no need to make such big changes to the ...