Merge pull request #737 from kostya/slice_before

Enumerable#slice_before from rubinius

lib-topaz/enumerable.rb

@@ -470,4 +470,35 @@ def chunk(initial_state = nil, &original_block)
       yielder.yield [previous, accumulate] unless accumulate.empty?
     end
   end
+
+  def slice_before(*args, &block)
+    arg = nil
+    if block
+      raise ArgumentError.new("wrong number of arguments (#{args.size} for 0..1)") if args.size > 1
+      if args.size == 1
+        has_init = true
+        arg = args[0]
+      end
+    else
+      raise ArgumentError.new("wrong number of arguments (#{args.size} for 1)") if args.size > 1
+      raise ArgumentError.new("wrong number of arguments (0 for 1)") if args.empty?
+      arg = args[0]
+      block = Proc.new{ |elem| arg === elem }
+    end
+    ::Enumerator.new do |yielder|
+      init = arg.dup if has_init
+      accumulator = nil
+      each do |elem|
+        start_new = has_init ? block.yield(elem, init) : block.yield(elem)
+        if start_new
+          yielder.yield accumulator if accumulator
+          accumulator = [elem]
+        else
+          accumulator ||= []
+          accumulator << elem
+        end
+      end
+      yielder.yield accumulator if accumulator
+    end
+  end
 end