I'm sure you know better, but at first glance this seems wrong. Reason: `main` is not itself a template, so `cast` is not a dependent name.

C++ compilers used to be liberal about accepting unnecessary instances of the `typename` keyword so lots of people would just sprinkle them everywhere. Modern versions of both Clang and GCC call this out.

The actual rule: https://en.cppreference.com/w/cpp/language/dependent_name#Th...