Reading the part about pure functions (including the extension [[gnu::pure]]) made me feel that this is a part where the C++ default is actually wrong. Not just because it could be better/hindsight/other languages have it/etc. but because it is in conflict with its own motto, don't pay for what you don't use. I really hope I can enable a compiler flag some time in the future that would make my variables const, and my functions pure by default.