If one wishes to be pedantic, constexpr is a C++-like language for generating C++ values at compile time and templates are a quite different language for doing the same thing (and some other things). The pitch of the comptime feature is that you can do all of the things you would do with templates and constexpr (and more things due to some limitations being relaxed and type introspection existing) in the language that is similar to the language you use for runtime code. You don't have to do anything in a weird metalanguage.