> The template metaprogramming C++ offers is the most powerful of any imperative language

I'm curious what languages you're comparing to here. Feels like it's only slightly more expressive than pure generics, but I admittedly haven't done much template metaprogramming myself. How does it compare to, say, Zig's comptime?

The problem with metaprogramming-heavy C++ codebases is always compilation times and obtuse error messages...

Template metaprogramming is sometimes very useful to get around C++'s language restrictions, but I tend to use it sparingly.

have you written about this anywhere, or hosting any examples?

C++ template metaprogramming is in some ways more powerful than Common Lisp macros, because it works at the type level: you can generate new types and dispatch into separate implementations by type. In contrast, Common Lisp type declarations are not available at macro expansion time unless you implement a full source-to-source translator in macros.