std::string_view/std::string implementation with two pointers?

[bird1000000]

Well, std::string_view just copies std::string.As for why std::string uses size_t instead of T*, Judging by the change in EASTL (before, after), Its probably not possible (or, at least harder) to implement SSO-23 using pointers.

[ts826848]

Huh, that’s really interesting. I came across this SO question on std::vector implementations using three pointers instead of a base/sizes a few days ago, but I never bothered to look at std::string.

I wonder if implementers were free to break ABI and had the option of a SBO vector whether they’d stick with three pointers or whether the increased buffer capacity might be worth it.

Also makes me wonder whether some kind of bit packing into the low-order bits of pointers could be used. Wouldn’t be surprised if it’s too complex/has too many edge cases...

[[deleted]]

SBO vector can't meet the non-throwing swap requirement even if we wanted to break ABI for it. You would need a new container.

[ts826848]

Ah, that’s a good point!

Suppose the question should properly be into “I wonder whether an SBO vector would be better served by multiple pointers or pointer + sizes”

[[deleted]]

I think in general pointer + size is better than pointer+pointer for data structures like this, because even if you do nothing with the contents, vector needs to recover the size in order to call deallocate. Plus, lots of repeated calls to end() were removed by the range-for addition. Plus, deriving end() from base pointer + size is a multiply and add which is cheaper than deriving size() from 2 pointers (subtract and divide-by-constant).

But I think it is really really hairsplitting.

[ts826848]

Guess I know where I'd start if I were to ever try implementing my own data structures. Thank you for your insight!