[diimdeep]

I think that everybody should instead read proposal that introduced this feature, P0479R2[1]

[1] https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p04...

and look at code in the wild

[2] https://github.com/search?q=[[likely]]+language%3Ac%2B%2B&ty...