C++ is at the very least less lazy than Zig. As an example, if you write some constexpr expression that evaluates a ternary and instantiates a function differently in the two prongs, both will be instantiated, even the one that doesn't end up in the final program. Yes, there are workarounds, but I didn't end up using them. I just moved the offending assert from compile time to runtime because this particular code was not that important.
But the question is if that's actually decisive in the slow compilation problem. The solution in an eager language for evaluating too much stuff is basically "more if statements". Same thing in C++ metaprogramming, use more "if constexpr". If that's all it took to fix C++ compile times, it would have been done a decade ago. The actual problem is all the stuff that you do actually use that has to get repeatedly inlined and optimized away for zero cost abstraction to work.
