Never realized concepts implied you can have multiple default constructors, that's hilarious. This is still a useful feature though. People complain a lot about

Never realized concepts implied you can have multiple default constructors, that's hilarious. This is still a useful feature though. People complain a lot about C++ corner cases, but this is one you would probably never hit in real code, and `requires` clauses does a lot to clarify type requirements and provide better error messages (instead of getting a ten page template stack trace ending in some extremely cryptic type requirement for some nested class, you just get a short error message at the require site, explaining why a certain type isn't valid).