knu	2017-10-22 21:25:34 +0900 (Sun, 22 Oct 2017)

  New Revision: 60360

  https://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=60360

  Log:
    Add `Set#reset`
    
    This method resets the internal state of a set after modification to
    existing elements, reindexing and deduplicating them. [Feature #6589]

  Modified files:
    trunk/lib/set.rb
    trunk/test/test_set.rb
Index: lib/set.rb
===================================================================
--- lib/set.rb	(revision 60359)
+++ lib/set.rb	(revision 60360)
@@ -477,6 +477,19 @@ class Set https://github.com/ruby/ruby/blob/trunk/lib/set.rb#L477
     @hash.eql?(o.instance_variable_get(:@hash))
   end
 
+  # Resets the internal state after modification to existing elements
+  # and returns self.
+  #
+  # Elements will be reindexed and deduplicated.
+  def reset
+    if @hash.respond_to?(:rehash)
+      @hash.rehash # This should perform frozenness check.
+    else
+      raise "can't modify frozen #{self.class.name}" if frozen?
+    end
+    self
+  end
+
   # Returns true if obj is a member of the set, and false otherwise.
   #
   # Used in case statements:
@@ -731,6 +744,11 @@ class SortedSet < Set https://github.com/ruby/ruby/blob/trunk/lib/set.rb#L744
               to_a
               super
             end
+
+            def rehash
+              @keys = nil
+              super
+            end
           END
         end
         # a hack to shut up warning
Index: test/test_set.rb
===================================================================
--- test/test_set.rb	(revision 60359)
+++ test/test_set.rb	(revision 60360)
@@ -761,6 +761,19 @@ class TC_Set < Test::Unit::TestCase https://github.com/ruby/ruby/blob/trunk/test/test_set.rb#L761
     assert_equal(3, set.size)
     assert_equal(array.uniq.sort, set.sort)
   end
+
+  def test_reset
+    [Set, Class.new(Set)].each { |klass|
+      a = [1, 2]
+      b = [1]
+      set = klass.new([a, b])
+
+      b << 2
+      set.reset
+
+      assert_equal(klass.new([a]), set, klass.name)
+    }
+  end
 end
 
 class TC_SortedSet < Test::Unit::TestCase

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