Reduce captures in ActiveSupport::Inflector#underscore

Author: nobu

activesupport/lib/active_support/inflector/methods.rb

@@ -98,7 +98,7 @@ def underscore(camel_cased_word)
       return camel_cased_word.to_s.dup unless /[A-Z-]|::/.match?(camel_cased_word)
       word = camel_cased_word.to_s.gsub("::", "/")
       word.gsub!(inflections.acronyms_underscore_regex) { "#{$1 && '_' }#{$2.downcase}" }
-      word.gsub!(/([A-Z])(?=[A-Z][a-z])|([a-z\d])(?=[A-Z])/) { ($1 || $2) << "_" }
+      word.gsub!(/(?<=[A-Z])(?=[A-Z][a-z])|(?<=[a-z\d])(?=[A-Z])/, "_")
       word.tr!("-", "_")
       word.downcase!
       word