Comment by pansa2
6 years ago
For a language whose purpose is high-performance, the std:: containers are an embarrassment. `deque` is slow, `map` is slow - so the language added `unordered_map` which is also slow...
Are any of the containers (other than `vector`) worth using in high-performance code?
I’m sympathetic to the game developers who I’ve heard say “we use C++, but nothing from std::”.
STL is mostly garbage, which is a big reason it's not used in places that actually need performance, both for build times and runtime.
Yes, it's embarrassing. I think it should be noted that the performance mantra is mostly for show with C++, though. The same people who spout it will also blatantly use pessimizing language features just because, when normal, procedural code would've done the job faster and ultimately simpler.
I think the performance overhead of a few things in C++ make sense, but in general you get performance in C++ by turning things off and abstaining from most of the features. Exceptions complicate mostly everything, so the best thing to do is to turn them off and not rely on anything that uses them, for example.
Modern C++ isn't fast and most of C++ wasn't even before the modern variant was invented. The C "subset" is.
> STL is mostly garbage, which is a big reason it's not used in places that actually need performance, both for build times and runtime.
It is NOT garbage. It is more than sufficient for the 99% of devs that need key in hand data structure and good enough performance (Meaning faster than 99% of over programming languages already).
If what you need is sub micro-second perf, then yes, redefined your data-structure.
BTW, you will very likely have to do that in any language anyway. Because it is impossible to design fast forever-living data structure. They (almost) all become obsolete when architectures evolve. Red-Black Trees where state of art DS, teached-at-school 10 years ago, they are useless garbage nowadays if you seek for performance.
> It is more than sufficient for the 99% of devs that need key in hand data structure and good enough performance (Meaning faster than 99% of over programming languages already).
I really don't get this argument. If you don't need pedal-to-the-metal performance then why are you using C++ in the first place? (Unless, of course, your answer is "legacy code".)
C++ is being touted as being high performance, but basically every standard data structure besides `std::vector` is garbage for high performance, pedal-to-the-metal code. And not only data structures - `std::regex`'s performance is bad, `std::unique_ptr` doesn't optimize as well as a plain pointers, no vendor has a best-in-class `std::hash` implementation (they're neither DoS-safe nor the fastest), etc.
> BTW, you will very likely have to do that in any language anyway. Because it is impossible to design fast forever-living data structure. They (almost) all become obsolete when architectures evolve.
Do you, though? Rust already replaced their standard hash map implementation with a completely different one which was faster, so it shows that it can be done.
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> Exceptions complicate mostly everything, so the best thing to do is to turn them off and not rely on anything that uses them, for example.
Look forward to all your users ignoring your return codes and never calling valid() on your objects that can only signal construction failed that way.
Also the impact of exceptions on performance is overblown, even in high perf situations:
https://news.ycombinator.com/item?id=20342183
Throwing is slow, but throwing is supposed to be rare. Don't use it as flow control.
About 1% of developers actually need to deliver µs fast code.
The remaining 99% are happy to be able to deliver fast enough portable code without having to reinvent data structures all the time.
Array is great as far as I know.
std::array is great except it's annoying to statically initialize. Really wish make_array or to_array were non-experimental a lot sooner (to_array finally did land in C++20 at least).
But yeah it does mean you can finally stop doing that silly `sizeof(a)/sizeof(a[0]);` trick.