Bug 16210 – std.utf.byUTF can be made into a bidirectional range

... for certain inputs at least. Currently it's only a forward range.

Assuming "ö" == [0xC3, 0xB6], which one version would be correct: a) behaviour of std.utf.byCodeUnit, just go by code units backward: "ö".byUTF!char().back == 0xB6 b) decode the character and return its first code unit: "ö".byUTF!char().back == 0xC3 Personally I thought the b) version is desired (docs says that byUTF encodes input), but at the moment it passes some inputs to byCodeUnit - it means for some ranges byUTF is bidirectional already and version a) applies.

(In reply to Jakub Łabaj from comment #1) > Assuming "ö" == [0xC3, 0xB6], which one version would be correct: > a) behaviour of std.utf.byCodeUnit, just go by code units backward: > "ö".byUTF!char().back == 0xB6 > > b) decode the character and return its first code unit: > "ö".byUTF!char().back == 0xC3 > > Personally I thought the b) version is desired (docs says that byUTF encodes > input), but at the moment it passes some inputs to byCodeUnit - it means for > some ranges byUTF is bidirectional already and version a) applies. Well damn. IMO B is more intuitive in all situations, so byUTF returning by byCodeUnit isn't want we really want. But because we can't break code, we would have to have B be the behavior only when some encoding has to be done inside of byUTF and clearly document this odd behavior.

Or we should implement another function e.g. byCodePoint which would behave as we want in all cases? For me it seems a better solution than function logic dependent on argument's type.

Or maybe add a templated switch which would default to the a), but allow to choose b)?

@vladchicos created dlang/phobos pull request #8183 "[DSSv3] Fix Issue 16210 - std.utf.byUTF can be made into a bidirectional range" fixing this issue: - Fix Issue 16210 - std.utf.byUTF can be made into a bidirectional range. https://github.com/dlang/phobos/pull/8183

@vladchicos created dlang/phobos pull request #8185 "[DSSv3] Fix Issue 19727 - std.algorithm.endsWith fails to compile while startsWith succeeds" fixing this issue: - Fix Issue 16210 - std.utf.byUTF can be made into a bidirectional range. https://github.com/dlang/phobos/pull/8185

dlang/phobos pull request #8183 "[DSSv3] Fix Issue 16210 - std.utf.byUTF can be made into a bidirectional range" was merged into master: - c76af8242253220d66a82616d64853ccb5ea8cfb by vladchicos: Fix Issue 16210 - std.utf.byUTF can be made into a bidirectional range. https://github.com/dlang/phobos/pull/8183