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。

例:

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

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

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

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