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authorBjörn Gustavsson <[email protected]>2017-02-01 16:25:47 +0100
committerBjörn Gustavsson <[email protected]>2017-02-02 12:18:54 +0100
commitdb442323e9e86528edeb7226d55404e290b088b3 (patch)
tree58248d652e7878947f2e75d1627a9fccecd35bb9 /plt
parentcce3120dd0021c5ab5bf8d5b4088e7364f678dda (diff)
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Make "~s" fail for Unicode atoms
26b59dfe67e introduced support for arbitrary Unicode characters in atoms. After that commit, it is possible to print any atom with a "~s" format string: 1> io:format("~s\n", ['спутник']). спутник Note that the same text as a string will fail: 2> io:format("~s\n", ["спутник"]). ** exception error: bad argument in function io:format/3 called as io:format(<0.53.0>,"~s\n", [[1089,1087,1091,1090,1085,1080,1082]]) Being more permissive for atoms is probably beneficial for io:format/2. However, for io_lib:format/2, the new behavior breaks this guarantee in the documentation for io_lib:format/2: If and only if the Unicode translation modifier is used in the format string (that is, ~ts or ~tc), the resulting list can contain characters beyond the ISO Latin-1 character range (that is, numbers > 255). The problem is that you can no longer be sure whether io_lib:format/2 will return an iolist that can be successfully passed to a port or iolist_to_binary/1. We see three solutions: 1. Keep the new behavior. That means that you can get non-iolist data when you use ~s for printing an atom, but a 'badarg' when printing Unicode strings. That is inconsistent, and it delays error detection if the result is passed to a port or iolist_to_binary/1. 2. Always allow Unicode characters for ~s. That would be incompatible, because ~s says that any binary is encoded in latin1, while ~ts says that any binary is encoded in UTF-8. To implement this solution, we could no longer support latin1 binaries; all binaries would have to be encoded in UTF-8. 3. Only allow ~s for atoms where all characters are less than 256. Require ~ts to print atoms such as 'спутник'. We reject solution 1 because it is slightly incompatible and is inconsistent. We reject solution 2 because it too incompatible. Therefore, this commit implements solution 3.
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