2 files changed, 19 insertions, 3 deletions
diff --git a/activesupport/lib/active_support/multibyte/chars.rb b/activesupport/lib/active_support/multibyte/chars.rb
index 99b974e4a7..ac61870871 100644
--- a/activesupport/lib/active_support/multibyte/chars.rb
+++ b/activesupport/lib/active_support/multibyte/chars.rb
@@ -93,7 +93,7 @@ module ActiveSupport #:nodoc:
         chars(Unicode.unpack_graphemes(@wrapped_string).reverse.flatten.pack('U*'))
       end
 
-      # Limit the byte size of the string to a number of bytes without breaking characters. Usable
+      # Limits the byte size of the string to a number of bytes without breaking characters. Usable
       # when the storage for a string is limited for some reason.
       #
       # Example:
@@ -102,7 +102,7 @@ module ActiveSupport #:nodoc:
         slice(0...translate_offset(limit))
       end
 
-      # Convert characters in the string to uppercase.
+      # Converts characters in the string to uppercase.
       #
       # Example:
       #   'Laurent, où sont les tests ?'.mb_chars.upcase.to_s # => "LAURENT, OÙ SONT LES TESTS ?"
@@ -110,7 +110,7 @@ module ActiveSupport #:nodoc:
         chars Unicode.upcase(@wrapped_string)
       end
 
-      # Convert characters in the string to lowercase.
+      # Converts characters in the string to lowercase.
       #
       # Example:
       #   'VĚDA A VÝZKUM'.mb_chars.downcase.to_s # => "věda a výzkum"
@@ -118,6 +118,14 @@ module ActiveSupport #:nodoc:
         chars Unicode.downcase(@wrapped_string)
       end
 
+      # Converts characters in the string to the opposite case.
+      #
+      # Example:
+      #    'El Cañón".mb_chars.swapcase.to_s # => "eL cAÑÓN"
+      def swapcase
+        chars Unicode.swapcase(@wrapped_string)
+      end
+
       # Converts the first character to uppercase and the remainder to lowercase.
       #
       # Example:
diff --git a/activesupport/lib/active_support/multibyte/unicode.rb b/activesupport/lib/active_support/multibyte/unicode.rb
index 94fb0a48aa..a0a8f3c97e 100644
--- a/activesupport/lib/active_support/multibyte/unicode.rb
+++ b/activesupport/lib/active_support/multibyte/unicode.rb
@@ -293,9 +293,17 @@ module ActiveSupport
         apply_mapping string, :uppercase_mapping
       end
 
+      def swapcase(string)
+        apply_mapping string, :swapcase_mapping
+      end
+
       # Holds data about a codepoint in the Unicode database
       class Codepoint
         attr_accessor :code, :combining_class, :decomp_type, :decomp_mapping, :uppercase_mapping, :lowercase_mapping
+
+        def swapcase_mapping
+          uppercase_mapping > 0 ? uppercase_mapping : lowercase_mapping
+        end
       end
 
       # Holds static data from the Unicode database