Add Set#compare_by_identity and Set#compare_by_identity?

* lib/set.rb (Set#compare_by_identity, Set#compare_by_identity?):
  New methods. [Feature #12210]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56589 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 20 insertions, 2 deletions

diff --git a/lib/set.rb b/lib/set.rb
index e77af5de2e..43c388ca90 100644
--- a/lib/set.rb
+++ b/lib/set.rb
@@ -3,7 +3,7 @@
 #
 # set.rb - defines the Set class
 #++
-# Copyright (c) 2002-2013 Akinori MUSHA <[email protected]>
+# Copyright (c) 2002-2016 Akinori MUSHA <[email protected]>
 #
 # Documentation by Akinori MUSHA and Gavin Sinclair.
 #
@@ -37,7 +37,8 @@
 # Set uses Hash as storage, so you must note the following points:
 #
 # * Equality of elements is determined according to Object#eql? and
-#   Object#hash.
+#   Object#hash.  Use Set#compare_by_identity to make a set compare
+#   its elements by their identity.
 # * Set assumes that the identity of each element does not change
 #   while it is stored.  Modifying an element of a set will render the
 #   set to an unreliable state.
@@ -91,6 +92,23 @@ class Set
     end
   end
 
+  # Makes the set compare its elements by their identity and returns
+  # self.  This method may not be supported by all subclasses of Set.
+  def compare_by_identity
+    if @hash.respond_to?(:compare_by_identity)
+      @hash.compare_by_identity
+      self
+    else
+      raise NotImplementedError, "#{self.class.name}\##{__method__} is not implemented"
+    end
+  end
+
+  # Returns true if the set will compare its elements by their
+  # identity.  Also see Set#compare_by_identity.
+  def compare_by_identity?
+    @hash.respond_to?(:compare_by_identity?) && @hash.compare_by_identity?
+  end
+
   def do_with_enum(enum, &block) # :nodoc:
     if enum.respond_to?(:each_entry)
       enum.each_entry(&block) if block