Daniel Lemire's blog

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Consider using constexpr static function variables for performance in C++

3 thoughts on “Consider using constexpr static function variables for performance in C++”

  1. Romin says:


    I wonder if the benchmark between std::string and std::string_view is 100% fair.

    Your functions that return std::string need to explicitly copy the grabbed string. If you make your “static const std::string” version return by reference, it really makes it as fast as the “static std::string_view” version.

    About code bloat, I fully agree that the constexpr version is better.

    Anyway, thanks for sharing!

    1. I agree that the performance (in terms of speed) is sometimes (but not always) identical.

  2. Juliean says:

    The reason why static and constexpr perform similar is that, most likely, the compiler will detect that the array is a constant expression (even if not specified), and remove it. This can be observed with your example-code in Godbolt. This is true for most code – a lot of the time, an optimizing compiler can do the same work regardless of whether a function is marked constexpr or not (as long as it can see the definition).

    constexpr is mainly used to enforce this, even in a debug-build (aside from all the other uses where non-constexpr function cannot be used to). constexpr also forced the functions definition to be visible when used.