Bug #17110: String.tr unexpected behaviour with backslash

• Status: Rejected
• Assignee: -
• Target version: -
• ruby -v: ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x64-mingw32]
• Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN

[theplen (Joey Sheets)]

"\\".tr("\\","A") works great, with "\\" becoming "A".

"\\".tr("\\C","AB") should also output "A", but instead outputs "\\".

[theplen (Joey Sheets)]

"\\".tr("\\","A") works great, with "\\" becoming "A"

"\\".tr("\\C","AB") should also output "A" but instead outputs "\\"

[sawa (Tsuyoshi Sawada)]

• Description updated (diff)

[mame (Yusuke Endoh)]

• Status changed from Open to Rejected

See the document.

The backslash character \ can be used to escape ^ or - and is otherwise ignored unless it appears at the end of a range or the end of the from_str or to_str:

https://docs.ruby-lang.org/en/2.7.0/String.html#method-i-tr

So you can write "\\".tr("C\\", "BA") according to the document.

This seems undocumented, but \ can be used to escape \, so you can also write "\\".tr("\\\\C", "AB").

[theplen (Joey Sheets)]

Is there no way to do change all backslashes to forward slashes and forward slashes to backslashes in the same tr command?

# Should result in "/\\" but instead results in "\\/" (unchanged)
"\\/".tr("\//","\\/")

[mame (Yusuke Endoh)]

p "\\/".tr("/\\\\", "\\\\/") #=> "/\\"

Unfortunately it is complicated, but \ is an escape character of string literal as well as an escape character of String#tr format, so it is unavoidable.

[theplen (Joey Sheets)]

Yusuke Endoh, thanks for clearing it up.