I'm curious - what you think of as a good example? I think of C++ templates & macros, which I would not describe as arising from restrictions?

Template metaprogramming in the absence of constexpr/concepts would be my guess.

That would be the relevant example.

Compile-time code restriction seems dumb. Programers can write any program they wish, stopping them for some ideological reason isnt effective. As with all the half-baked metaprogramming people restort to anyway.

Traits are more restricted in what they can do than Templates, so the original quote does not apply here

Template metaprogramming is the idea of executing arbitrary logic at compile time using the template system as your programming language. The replacement for template metaprogramming is a solid compile-time execution model, not a traits system.

Excellent point!