extract.rb

class Enumerator
  def extract(&blk)
    self.each do |obj|
      blk.call(*blk.parameters.map(&:last).map {|attr| obj.send(attr)})
    end
  end
end

Treasure = Struct.new(:coins, :gems)

treasures = [
  Treasure.new(100, %w[emerald ruby]),
  Treasure.new(70,  %w[amethyst], [])
]

treasures.each.extract do |coins|
  coins # => 100, 70
end

treasures.each.extract do |gems|
  gems # => ["emerald", "ruby"], ["amethyst"]
end

Sure this compiles ?

I had to fix it for ruby 2.0 :

/Users/peter_v/t $ ruby -v
ruby 2.0.0p247 (2013-06-27 revision 41674) [x86_64-darwin12.4.0]

/Users/peter_v/t $ git diff
diff --git a/t.rb b/t.rb
index 6fcf6dd..32c001c 100644
--- a/t.rb
+++ b/t.rb
@@ -10,13 +10,13 @@ Treasure = Struct.new(:coins, :gems)

 treasures = [
   Treasure.new(100, %w[emerald ruby]),
-  Treasure.new(70, %w[amethyst], [])
+  Treasure.new(70, %w[amethyst])
 ]

 treasures.each.extract do |coins|
-  coins # => 100, 70
+  puts coins # => 100, 70
 end

 treasures.each.extract do |gems|
-  gems # => ["emerald", "ruby"], ["amethyst"]
+  puts gems # => ["emerald", "ruby"], ["amethyst"]
 end
/Users/peter_v/t $ ruby t.rb 
100
70
emerald
ruby
amethyst

you're right, that empty array is a leftover from earlier code.

Thanks for the confirmation.