Named captures "conflict" warning is unnecessary and limits uses of named captures
There's currently a warning whenever a named capture in a regular expression has the same name as an already-declared local variable:
$ ruby23 -v -e 'x = 1; /(?<x>foo)/ =~ "foo"' ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-darwin14] -e:1: warning: named capture conflicts a local variable - x
It also warns if you have two expressions using the same named capture:
$ ruby23 -v -e '/(?<x>foo)/ =~ "foo"; /(?<x>foo)/ =~ "foo"' ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-darwin14] -e:1: warning: named capture conflicts a local variable - x
I do not believe either of these warnings are useful, since the only option for fixing them is to use a new variable name for every named capture.
I have a few more reasons, as well:
- Using the same named capture on both the "then" and "else" branches of an "if" statement will produce a warning. Changing one of the names requires additional work to join the to branches back together (since now there's no single variable resulting from them).
- It is not possible to initialize a variable with the same name as a named capture.
- The pattern that results from this warning is renaming a capture something like "name2" and then having "name = name2" after the match. Ugly.
Risks of removing the warning:
- When a named capture writes to an already-declared variable, that may surprise a user.
I think this risk is very low, especially since you'd have to turn on verbose mode to even see the warning.
Updated by headius (Charles Nutter) over 4 years ago
I have worked around this for now in JRuby by modifying the warning to only fire if a named capture was previously declared as something other than a named capture.
The commit to JRuby is here: https://github.com/jruby/jruby/commit/3ebc198860905084231d2a1356ea46718b86f2b0
It resolves the verbose noise issue we had with our date/format implementation.
I propose that the warning should only fire when it is a mixed-use variable, i.e. it is potentially assigned both as a named capture and as a normal local variable.
I'd actually like to get rid of it altogether, but it's really just this mixed-use case that needs a warning.
Updated by nobu (Nobuyoshi Nakada) over 4 years ago
- Status changed from Open to Closed
Applied in changeset r55396.
parse.y: no named capture conflict warnings
- parse.y (reg_named_capture_assign_iter): remove named capture conflict warnings. it is just annoying rather than useful. [ruby-core:75416] [Bug #12359]