consider using size_t instead of int for length

[iljavs]

Currently str uses (signed) int for all lengths/sizes/capacity. when handling large strings (~2g and up, which is fairly realistic these days on 64 bit machines) signedness issues occur and memory corruption happens in various places.

[ocornut]

The type was designed to be compact.
We currently don't even use 32-bits for size but 21-bits which is even lower, so your statement seems to be coming from a strictly theoretical position rather than actual need, since you didn't realize it was already capped to 21-bits.

The current packing made sense on 32-bits targets but effectively we have 4 bytes of unused padding on 64-bits targets. There is a todo to actually update to 32-bit storage for size, but I suppose we could use 53 bits just as well..