Feature #19315
Updated by Eregon (Benoit Daloze) over 1 year ago
CRuby should implement lazy substrings, i.e., "abcdef"[1..3] must not copy bytes.
Currently CRuby only reuse the char* if the substring is until the end of the buffer.
But it should also work wherever the substring starts and ends.
Yes, it means RSTRING_PTR() might need to allocate to \0-terminate, so be it, it's worth it.
There is already code for this (`SHARABLE_MIDDLE_SUBSTRING`), but it's disabled by default and `RSTRING_PTR()` needs to be changed to deal with this.
It seems a good idea to introduce a variant of `RSTRING_PTR` which doesn't guarantee \0-termination, so such callers can then use the existing bytes always without copy.
There are countless workarounds for this missing optimization, all not worth and all less readable:
* https://bugs.ruby-lang.org/issues/19314
* https://bugs.ruby-lang.org/issues/18598#note-3
* https://github.com/ruby/net-protocol/pull/14
* Manual lazy substrings which track string + index + length
* More but I don't remember all now, feel free to comment or link more urls/tickets.