Add `Set#reset`

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

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60360 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/set.rb

@@ -477,6 +477,19 @@ class Set
     @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
               to_a
               super
             end
+
+            def rehash
+              @keys = nil
+              super
+            end
           END
         end
         # a hack to shut up warning

test/test_set.rb

@@ -761,6 +761,19 @@ class TC_Set < Test::Unit::TestCase
     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