I know that, but that's a rather elaborate way of doing the main thing sets do, and you have to repeat the name of the set twice. Fortunately C++20 added set.co

I know that, but that's a rather elaborate way of doing the main thing sets do, and you have to repeat the name of the set twice. Fortunately C++20 added set.contains(x). Of course set.count(x) also already existed but some would prefer set.find(x) != set.end() anyway for <reasons>, and it's the fault of the language's design to cause such opinions in the first place imho.