alt Hacker NewsIn practice, C means you end up with generic data structures with pointers to what they contain, rather than being inline.
You do see a lot of macro use to deal with this, but that is just primitive, non-typesafe metaprogramming, and it gets unwieldy enough that in practice, you see people add an extra pointer. This is why it gets slower.
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If you need callbacks and generics, you're not writing performance code.
99% of code in the wild is comically inefficient and is doing the wrong thing, using way too generic data structures and algorithms for very concrete problems. C++ templates may be one way to make comically slow code faster by spending a lot of compile time. But it's often much quicker to just write straightforward concrete code that the compiler can easily optimize.
IMO C++ makes for slow programs for the sole fact that it compiles so slow (if you use its modern features), so you have much less time to actually iterate and improve.
In practice, I see people write very performance C code where it matters, while moving on quickly where it does not. C++ code is often highly templated with annoying compile times, but still often slow because it still does not use the right data structures, and the amount of instruction bloat by specializing everything does not help for anything which is not a toy benchmark.