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This reverts commit 5cc7f12.
…the returned pointer is invalidated by any subsequent unsharing operation
…_MIDDLE_SUBSTRING
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Summary
This is a PoC for enabling
SHARABLE_MIDDLE_SUBSTRING=1(proposed in https://bugs.ruby-lang.org/issues/19315), which allows zero-copy shared substrings for arbitrary ranges (not just tail ranges).The key challenge is that a shared middle substring may not have a null terminator at
ptr[len], soRSTRING_PTR()must lazily ensure termination before returning the pointer. This PoC implements that guarantee.Thinking
RSTRING_GETMEMinternally callsRSTRING_PTR(), so callers that only need the pointer+length (no null termination) also pay the overhead. ARSTRING_GETMEM_STARTvariant could be added to allow gradual migration of internal callers, while keepingRSTRING_GETMEMfor backward compatibility with C extensions.Testing
Existing tests pass without modification. No new test cases are added in this PoC; proper coverage for middle-shared substrings and multi-byte terminators should be added before merging.