c# - Why does the async keyword exist

Question

Browsing through the channel 9 msdn videos I found the following unanswered comment and was hoping someone could possibly explain it?

I dont get the point of the async keyword. Why not just allow the await keyword anytime the method returns Task, just like iterators can yield return on any method that returns an IEnumerable.

I'm sure there is a good reason, I'd just like to understand why the above suggestion was not possible.

Answer 1

It was introduced mainly to avoid backward compatibility issues. If the async-ness of a method must be inferred by the compiler (that would be through the detection of await keywords), then there are subtle scenarios where existing code would suddenly be treated differently, notably when you have identifiers (variable or function names called await).

A full explanation is here: https://docs.microsoft.com/en-us/archive/blogs/ericlippert/asynchrony-in-c-5-part-six-whither-async