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RedShift1 a day ago

Which characters are not available in UTF-8 that warrant using WTF-8?

badmintonbaseba a day ago | parent | next [-]

Invalid UTF-16 with unpaired surrogates. Or rather WTF-8 is an alternate encoding of UCS-2. The subset of UCS-2 that is valid UTF-16 encodes to valid UTF-8 when encoded with WTF-8. The encoding is invertible, valid UTF-8 decodes to valid UTF-16, otherwise any byte sequence decodes to UCS-2.

chrismorgan a day ago | parent | prev [-]

Just read the abstract:

> WTF-8 (Wobbly Transformation Format − 8-bit) is a superset of UTF-8 that encodes surrogate code points if they are not in a pair. It represents, in a way compatible with UTF-8, text from systems such as JavaScript and Windows that use UTF-16 internally but don’t enforce the well-formedness invariant that surrogates must be paired.

RedShift1 a day ago | parent [-]

Ok, but in practice, what does this mean for the characters? Are there certain characters unavailable?

chrismorgan a day ago | parent | next [-]

It’s the unpaired surrogate code points. That’s the whole thing. It’s about encoding ill-formed UTF-16, which is distressingly common in the real world.

numpad0 a day ago | parent | prev [-]

broken emojis? There apparently are known issues that some frameworks break Unicode at wrong boundaries, maybe the author saw it regularize into a deeper mess

masklinn a day ago | parent [-]

It’s not just broken emoji, it’s straight up broken content: UTF-8 can not represent unpaired surrogates.

WTF-8 is necessary for Rust’s compatibility with Windows filesystems (it underlines OsString on Windows) as e.g. file names are sequences of UTF-16 code units (and thus may contain unpaired surrogates).