Bug #21288: StringScanner#named_captures overrides matched captures with unmatched captures - Ruby - Ruby Issue Tracking System

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Bug #21288

closed

StringScanner#named_captures overrides matched captures with unmatched captures

Added by robotdana (Dana Sherson) 5 days ago. Updated 4 days ago.

Status:

Closed

Assignee:

kou (Kouhei Sutou)

Target version:

ruby -v:

ruby 3.4.3 (2025-04-14 revision d0b7e5b6a0) +PRISM [x86_64-darwin23]

Backport:

3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN

[ruby-core:121747]

Description

StringScanner#named_captures operates inconsistently with MatchData#named_captures when there is the same name used in multiple branches
For Regexp it uses the value that was captured (useful). For StringScanner it uses the one last in source order.

require 'strscan'
re = /(?<test>value)|(?<test>other branch)/
scanner = StringScanner.new("value")
scanner.scan(re)
scanner.named_captures #=> {"test" => nil}
"value".match(re).named_captures # => {"test" => "value"}


scanner = StringScanner.new('other branch')
scanner.scan(re)
scanner.named_captures #=> {"test" => "other branch"}
"other branch".match(re).named_captures # => {"test" => "other branch"}