From d67ed5226a7f96bdb69f6718f389790c1735230e Mon Sep 17 00:00:00 2001
From: gogotanaka <mail@tanakakazuki.com>
Date: Fri, 9 Jan 2015 17:07:18 -0800
Subject: [PATCH 1/4] Implement set#power
To: https://bugs.ruby-lang.org/

---
 lib/set.rb | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/lib/set.rb b/lib/set.rb
index d1ea6d8..f3c0358 100644
--- a/lib/set.rb
+++ b/lib/set.rb
@@ -513,6 +513,22 @@ class Set
     end
   end

+  # Returns set of all subsets of +self+.
+  #
+  # e.g.:
+  #
+  #   require 'set'
+  #   set = Set[1, 2].power
+  #   p set     # => #<Set: {#<Set: {}>,
+  #             #            #<Set: {1}>,
+  #             #            #<Set: {2}>,
+  #             #            #<Set: {1, 2}>}>
+  def power
+    (0 .. 2 ** length - 1).map { |n|
+      select.with_index { |_, i| (n >> i) & 1 == 1 }.to_set
+    }.to_set
+  end
+
   InspectKey = :__inspect_key__         # :nodoc:

   # Returns a string containing a human-readable representation of the
--
gogotanaka