Prefill Storage with zero values

Only if Storage already has some data.
Disable empty and prefill feature if given lenght is 0.

lib/rubella/storage.rb

@@ -10,23 +10,37 @@ module Rubella
     attr_reader :data
     attr_reader :length
 
-    def initialize data, length = nil
-      @data = data
+    def initialize data, length = 0
+      @data       = data
       self.length = length
     end
 
     # Defines the length of the Storage.
+    #
     # Be careful, if your Storage has more entries, tha the new length, the
-    # oldest entries will immediately be dropped.
+    # oldest entries will immediately be dropped. If your Storage has less
+    # entries, it will be filled up with empty entries.
+    # Happens only if data has entries.
+    #
+    # Setting the length to 0 will disable this feature
+    #
+    # @param length Integer The size of the storage
+    # @return Integer The new size
     #
     def length= length
       @length = length
 
-      # Drop entries, if more than new length
-      if @length.kind_of? Integer
+      # Use length only, if length is valid
+      if @length != 0 and @data.length != 0
+        # Drop entries, if more than new length
         while @data.length > @length
           @data.pop
         end
+        # Prefill with empty content, if less than new length
+        dummy_data = Array.new(@data[0].length, 0)
+        while @data.length < @length
+          @data.unshift dummy_data
+        end
       end
       
       @length