[librt] Add minimal librt.strings.StringWriter class (experimental) #20588
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According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅ |
p-sawicki
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Jan 15, 2026
JukkaL
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michaelm-openai
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…ython#20588) It can be used to build a string from code points (via `append` method) and strings (via `write`). It's similar to `BytesWriter`, but it has to keep track of the kind of string being created (1/2/4 bytes per code point). I've optimized `append` but there are no mypyc primitives yet, so performance is still bad. I'll add mypyc primitives in a follow-up PR and do further optimizations as needed. There is no `truncate` or `__setitem__`, unlike `BytesWriter`, since these could require the recomputation of kind, and this would be inefficient. My current thinking is that we won't support these. I used LLM assist, especially for tests, but manually reviewed all changes.
michaelm-openai
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Jan 16, 2026
…ython#20588) It can be used to build a string from code points (via `append` method) and strings (via `write`). It's similar to `BytesWriter`, but it has to keep track of the kind of string being created (1/2/4 bytes per code point). I've optimized `append` but there are no mypyc primitives yet, so performance is still bad. I'll add mypyc primitives in a follow-up PR and do further optimizations as needed. There is no `truncate` or `__setitem__`, unlike `BytesWriter`, since these could require the recomputation of kind, and this would be inefficient. My current thinking is that we won't support these. I used LLM assist, especially for tests, but manually reviewed all changes.
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It can be used to build a string from code points (via
appendmethod) and strings (viawrite). It's similar toBytesWriter, but it has to keep track of the kind of string being created (1/2/4 bytes per code point).I've optimized
appendbut there are no mypyc primitives yet, so performance is still bad. I'll add mypyc primitives in a follow-up PR and do further optimizations as needed.There is no
truncateor__setitem__, unlikeBytesWriter, since these could require the recomputation of kind, and this would be inefficient. My current thinking is that we won't support these.I used LLM assist, especially for tests, but manually reviewed all changes.