From ad78cf4ea8613c7e1790c5e3a2718a35fe32115f Mon Sep 17 00:00:00 2001
From: knu <knu@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Fri, 19 Jul 2013 02:22:11 +0000
Subject: [PATCH] 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        |  5 +++++
 NEWS             |  4 ++++
 lib/set.rb       | 10 ++++++++++
 test/test_set.rb |  3 +++
 4 files changed, 22 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index ec3c88fed0..7f95617f07 100644
--- a/ChangeLog
+++ b/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
diff --git a/NEWS b/NEWS
index 4594fc76af..f5fe38838d 100644
--- a/NEWS
+++ b/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.
diff --git a/lib/set.rb b/lib/set.rb
index a9aa7e7936..47fcc3efc7 100644
--- a/lib/set.rb
+++ b/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)
diff --git a/test/test_set.rb b/test/test_set.rb
index 26950c3e30..cbf4eb0234 100644
--- a/test/test_set.rb
+++ b/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)