Issue #19315 has been updated by himura467 (Akito Shitara). Eregon (Benoit Daloze) wrote in #note-22:
What's the problem?
If `RSTRING_END()` remains unchanged, it can cause inconsistency due to the undefined evaluation order of C. This happens if `RSTRING_END()` is evaluated before `RSTRING_PTR()` in expressions like `search_nonascii(RSTRING_PTR(dest), RSTRING_END(dest))`. Given that this pattern actually appears in several places within the Ruby core, I think we should preserve backward compatibility here to be safe. Ref: https://github.com/ruby/ruby/blob/2ff671c93d337cc7c4793f9958557f3f8f4eb623/s... ---------------------------------------- Feature #19315: Lazy substrings in CRuby https://bugs.ruby-lang.org/issues/19315#change-117461 * Author: Eregon (Benoit Daloze) * Status: Open ---------------------------------------- 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/