Define Set#to_set so that aSet.to_set returns self.

* lib/set.rb (Set#to_set): Define Set#to_set so that aSet.to_set
  returns self. [Fixes GH-359]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42051 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,8 @@
+Fri Jul 19 11:16:54 2013  Akinori MUSHA  <knu@iDaemons.org>
+
+	* lib/set.rb (Set#to_set): Define Set#to_set so that aSet.to_set
+	  returns self. [Fixes GH-359]
+
 Fri Jul 19 11:10:23 2013  Zachary Scott  <e@zzak.io>
 
 	* lib/rake/*: [DOC] Capitalize "Ruby" in documentation

NEWS

@@ -137,6 +137,10 @@ with all sufficient information, see the ChangeLog file.
 
 === Stdlib compatibility issues (excluding feature bug fixes)
 
+* Set
+  * incompatible changes:
+    * Set#to_set now returns self instead of generating a copy.
+
 * URI
   * incompatible changes:
     * URI.decode_www_form follows current WHATWG URL Standard.

lib/set.rb

@@ -148,6 +148,16 @@ class Set
     @hash.keys
   end
 
+  # Returns self if no arguments are given.  Otherwise, converts the
+  # set to another with klass.new(self, *args, &block).
+  #
+  # In subclasses, returns klass.new(self, *args, &block) unless
+  # overridden.
+  def to_set(klass = Set, *args, &block)
+    return self if instance_of?(Set) && klass == Set && block.nil? && args.empty?
+    klass.new(self, *args, &block)
+  end
+
   def flatten_merge(set, seen = Set.new) # :nodoc:
     set.each { |e|
       if e.is_a?(Set)

test/test_set.rb

@@ -625,6 +625,9 @@ class TC_Enumerable < Test::Unit::TestCase
     assert_instance_of(Set, set)
     assert_equal([-10,-8,-6,-4,-2], set.sort)
 
+    assert_same set, set.to_set
+    assert_not_same set, set.to_set { |o| o }
+
     set = ary.to_set(SortedSet)
     assert_instance_of(SortedSet, set)
     assert_equal([1,2,3,4,5], set.to_a)