For those who don’t know, much of the fmt library interface has been standardized in C++20 as std::format. It’s a great library, and a very efficient alternative to ostream and friends.
Concepts took, what, the best part of 20 years and the end result is just OK. Unless there's something I'm missing the system as standardized in C++20 just seems overcooked - not very elegant while also introducing a lot of new legalese in the standard. The system D uses seems to be much simpler (and more powerful in the sense that it effectively moves template constraints into the library - doesn't require updating as traits change) i.e.
template<typename T>
if(constexprConditionOnT<T>)
void toy(T x) {}I can send you the turd of a PhD thesis that was left after my doctorate was bombed by the removal of concepts from C++0x.