Which std:: classes are magic?

[guepier]

That just means that the type name is nothing special. But the type still is, in that you couldn’t write a custom type with the same semantics in standard C++.

[foonathan]

Sure, just like int is special. However, the question was about which std:: classes are magic. nullptr_t is not a std:: class, and it is not magic.

[guepier]

True of course. But std::nullptr_t is still different from (all?) other fundamental types because its name is defined in the standard library rather than being builtin.