While constexpr was introduced in C++11, it was initially very limited -- a constexpr function could only consist of a single return statement, for example. It was only in C++14 that things like variable declarations and loops were allowed, and constexpr programming became practical.

> Were there particular features of 17 that you were able to benefit from?

I used std::variant from C++17 for polymorphism, as a workaround for the fact that you can't have constexpr virtual functions (these have since been proposed for C++20). I also used `std::optional` when testing for intersections between a ray and a "thing", but it would have been possible to structure the code in such a way that this wasn't necessary (for example, by using a bool return value and an out parameter).

Lastly, I used constexpr lambdas (new in C++17) though again, it would have been possible to do things differently so these weren't required -- and indeed I did have to work around the fact that Clang (at the time) didn't support evaluating capturing lambdas at compile-time.