[andrewflnr]

Concepts did not actually make it into the standard. I vaguely recall they were cut at the last minute or something.

[suby]

Concepts are in C++20. I don't know the specifics but it's my understanding that the version we got is stripped down in comparison to the original proposal.

[andrewflnr]

Oh, woops. Maybe they I only updated my belief before 2020. OP is right about one thing, cppreference is great. https://en.cppreference.com/w/cpp/language/constraints