Issue #20407 has been updated by naruse (Yui NARUSE). Since this feature is not widely used and will not be widely used, how do we keep this as is? After for a while, this feature should be removed like $KCODE and other deprecated encoding features. ---------------------------------------- Misc #20407: Question about applying encoding modifier to an interpolated Regexp https://bugs.ruby-lang.org/issues/20407#change-109070 * Author: andrykonchin (Andrew Konchin) * Status: Open ---------------------------------------- I am wondering how Regexp encoding modifiers (u, s, e, n) interfere in encoding negotiation of parts/fragments in an interpolated Regexp literal. Examples #1 ```ruby # encoding: us-ascii # Unicode: Ф - U+0424 # windows-1251: Ф - 0xD4 # without encoding modifier puts /a #{ "\xd4".force_encoding("windows-1251") } c/.encoding # Windows-1251 puts /a #{ "b".encode("windows-1251") } c/.encoding # US-ASCII puts /a #{ "\u0424".force_encoding("UTF-8") } c/.encoding # UTF-8 puts /a #{ "\xc2\xa1".b } c/.encoding # ASCII-8BIT # with encoding modifier puts /a #{ "\xd4".force_encoding("windows-1251") } c/e.encoding # Windows-1251 puts /a #{ "b".encode("windows-1251") } c/e.encoding # EUC-JP puts /a #{ "\u0424".force_encoding("UTF-8") } c/e.encoding # UTF-8 puts /a #{ "\xc2\xa1".b } c/e.encoding # ASCII-8BIT # string interpolation puts "a #{ "\xd4".force_encoding("windows-1251") } c".encoding # Windows-1251 puts "a #{ "b".encode("windows-1251") } c".encoding # Windows-1251 puts "a #{ "\u0424".force_encoding("UTF-8") } c".encoding # UTF-8 puts "a #{ "\xc2\xa1".b } c".encoding # ASCII-8BIT ``` Example #2 ```ruby # encoding: utf-8 # windows-1251: Ф - 0xD4 # unicode: Ф - U+0424 # without encoding modifier puts /a #{ "\xd4".force_encoding("windows-1251") } c/.encoding # Windows-1251 puts /a #{ "b".encode("windows-1251") } c/.encoding # US-ASCII puts /a #{ "\u0424".force_encoding("UTF-8") } c/.encoding # UTF-8 puts /a #{ "\xc2\xa1".b } c/.encoding # ASCII-8BIT # with encoding modifier puts /a #{ "\xd4".force_encoding("windows-1251") } c/e.encoding # Windows-1251 puts /a #{ "b".encode("windows-1251") } c/e.encoding # EUC-JP puts /a #{ "\u0424".force_encoding("UTF-8") } c/e.encoding # UTF-8 puts /a #{ "\xc2\xa1".b } c/e.encoding # ASCII-8BIT # string interpolation puts "a #{ "\xd4".force_encoding("windows-1251") } c".encoding # Windows-1251 puts "a #{ "b".encode("windows-1251") } c".encoding # UTF-8 puts "a #{ "\u0424".force_encoding("UTF-8") } c".encoding # UTF-8 puts "a #{ "\xc2\xa1".b } c".encoding # ASCII-8BIT ``` In the examples above the `e` modifier changes Regexp's encoding only in one case when Regexp's encoding would be `US-ASCII` without the modifier: ```ruby # encoding: us-ascii puts /a #{ "b".encode("windows-1251") } c/.encoding # US-ASCII puts /a #{ "b".encode("windows-1251") } c/e.encoding # EUC-JP ``` ```ruby # encoding: utf-8 puts /a #{ "b".encode("windows-1251") } c/.encoding # US-ASCII puts /a #{ "b".encode("windows-1251") } c/e.encoding # EUC-JP ``` And the `e` modifier doesn't change Regexp's final encoding in all the other cases either Regexp's encoding without modifier is a file source encoding or `ASCII-8BIT`. Looking at the following example: ```ruby # encoding: us-ascii # without modifier p /\xc2\xa1 #{ "a" }\xc2\xa1/.encoding # ASCII-8BIT p /a #{ "\xc2\xa1".force_encoding("EUC-JP") } b/.encoding # EUC-JP p /a #{ "\xc2\xa1".b } b/.encoding # ASCII-8BIT # with modifier p /\xc2\xa1 #{ "a" }\xc2\xa1/e.encoding # EUC-JP p /a #{ "\xc2\xa1".force_encoding("EUC-JP") } b/e.encoding # EUC-JP p /a #{ "\xc2\xa1".b } b/e.encoding # ASCII-8BIT ``` we can notice that the `e` modifier changes `ASCII-8BIT` to `EUC-JP` in the first case (`/\xc2\xa1 #{ "a" }\xc2\xa1/`) but doesn't in the third one (`/a #{ "\xc2\xa1".b } b/`). So I assume that the `e` modifier could be applied to the Regexp fragments (`\xc2\xa1` and `\xc2\xa1`) before encoding negotiation and not to the whole result after negotiation. Could you please clarify how it works? -- https://bugs.ruby-lang.org/