Issue #19315 has been updated by Dan0042 (Daniel DeLorme). duerst (Martin Dürst) wrote in #note-12:
Pat Shaughnessy in his blog describes exactly the same thing as Benoit Daloze above: Ruby shares string data as long as the ends of the strings align.
On first skimming the blog I actually didn't notice that. It's mentioned in one sentence and everything else is about how great Ruby is for avoiding unneeded allocations thanks to copy-on-write. I realize that `RSTRING_PTR` is used everywhere, but would it be in the realm of possibility to deprecate it and replace it by something like `RSTRING_CSTR` and `RSTRING_PSTR`. ---------------------------------------- Feature #19315: Lazy substrings in CRuby https://bugs.ruby-lang.org/issues/19315#change-103627 * Author: Eregon (Benoit Daloze) * Status: Open * Priority: Normal ---------------------------------------- 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 it with lazy substring 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. -- https://bugs.ruby-lang.org/