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> Small vectors break iterator guarantees, for one thing. It only breaks swap of the container itself during iteration. Which is a super niche condition. And
by kllrnohj 7y ago
> Small vectors break iterator guarantees, for one thing.
It only breaks swap of the container itself during iteration. Which is a super niche condition.
And that swap also invalidates some of std::vector's iterators as well - specifically the end() iterator.
> They also really only make sense for tiny objects (ints, etc.) given you don't want a pickup truck's worth of data on your stack. They're most definitely not general-purpose.
Of course they are still general-purpose. They can (and do) specialize on the size of the object being contained. The only reason std::vector doesn't also have SSO is because it's an ABI break. Not because it's better in some way or less fragile. Legacy is the only reason.
- mehrdadn 7y ago> And that swap also invalidates some of std::vector's iterators as well - specifically the end() iterator. And they don't invalidate the iterators that point to actual elements, which was kind of the entire point I was making. Don't let that stop you from trying to make it look like I'm just blurting out nonsense, though.
- kllrnohj 7y agoYou made a broad, vague claim that iterator guarantees were broken. You misrepresented it as being a much larger issue that it actually is. Nearly all iterator guarantees are not broken. One very specific guarantee in one very specific case is, that's it. And it's a rare, not general, case at that, making the trade-off necessary to achieve it a bad default.
- gpderetta 7y agoreturning, moving, swapping a small vector would break any pointer to an element. That's a big deal. Interior pointers are used all the time (that's, more than performance, the primary reason that reserve exist).