instance method Regexp#fixed_encoding?

正規表現が任意の ASCII 互換エンコーディングとマッチ可能な時に false を返します。

# -*- coding:utf-8 -*-

r = /a/
p r.fixed_encoding?                             # => false
p r.encoding                                    # => #<Encoding:US-ASCII>
p r =~ "\u{6666} a"                             # => 2
p r =~ "\xa1\xa2 a".force_encoding("euc-jp")    # => 2
p r =~ "abc".force_encoding("euc-jp")           # => 0

r = /a/u
p r.fixed_encoding?                             # => true
p r.encoding                                    # => #<Encoding:UTF-8>
p r =~ "\u{6666} a"                             # => 2
begin
  r =~ "\xa1\xa2".force_encoding("euc-jp")
rescue => e
  e.class                                       # => Encoding::CompatibilityError
end
p r =~ "abc".force_encoding("euc-jp")           # => 0

r = /\u{6666}/
p r.fixed_encoding?                             # => true
p r.encoding                                    # => #<Encoding:UTF-8>
p r =~ "\u{6666} a"                             # => 0
begin
  r =~ "\xa1\xa2".force_encoding("euc-jp")
rescue => e
  e.class                                       # => Encoding::CompatibilityError
end
p r =~ "abc".force_encoding("euc-jp")           # => nil