add nesting height calculation

lib/nested_multimap.rb

@@ -47,6 +47,33 @@ def each_association
     end
   end
 
+  def each_container_with_default
+    each_container = Proc.new do |container|
+      if container.respond_to?(:each_container_with_default)
+        container.each_container_with_default do |value|
+          yield value
+        end
+      else
+        yield container
+      end
+    end
+
+    hash_each_pair { |_, container| each_container.call(container) }
+    each_container.call(default)
+
+    self
+  end
+
+  def containers_with_default
+    containers = []
+    each_container_with_default { |container| containers << container }
+    containers
+  end
+
+  def height
+    containers_with_default.max { |a, b| a.length <=> b.length }.length
+  end
+
   def inspect
     super.gsub(/\}$/, ", nil => #{default.inspect}}")
   end

spec/nested_multimap_spec.rb

@@ -105,6 +105,19 @@
     ]
   end
 
+  it "should iterate over each container plus the default" do
+    a = []
+    @map.each_container_with_default { |container| a << container }
+    a.should == [
+      [100],
+      [200, 300],
+      [200],
+      [400, 500],
+      [500],
+      []
+    ]
+  end
+
   it "should iterate over each key" do
     a = []
     @map.each_key { |key| a << key }
@@ -131,13 +144,21 @@
     @map.containers.should == [[100], [200, 300], [400, 500]]
   end
 
+  it "should list all containers plus the default" do
+    @map.containers_with_default.should == [[100], [200, 300], [200], [400, 500], [500], []]
+  end
+
   it "should return array of keys" do
     @map.keys.should == ["a", ["b", "c"], ["b", "c"], ["c", "e"], ["c", "e"]]
   end
 
   it "should list all values" do
     @map.values.should == [100, 200, 300, 400, 500]
   end
+
+  it "should return the distance to the deepest nesting level" do
+    @map.height.should == 2
+  end
 end