dot method alteration similar to git, prevents alteration of non leaf settings

lib/hobo/config.rb

@@ -1,4 +1,6 @@
 module Hobo
+  
+  
   module_function
 
   def config
@@ -9,8 +11,21 @@ module Hobo
     @@alterable_config
   end
 
-  def set_config!(hash)
+  def config!(hash)
     @@alterable_config = hash.dup
     @@config = hash.freeze
   end
+
+  def set_config_value(chain, val, cfg=@@alterable_config)
+    keys = chain.split('.')
+    key = keys.shift.to_sym
+    if keys.empty? 
+      raise InvalidSettingAlteration if cfg[key].instance_of?(Hash)
+      return cfg[key] = val if keys.empty?
+    end
+
+    set_config_value(keys.join('.'), val, cfg[key])    
+  end
+
+  class InvalidSettingAlteration < StandardError; end
 end

lib/hobo/env.rb

@@ -23,7 +23,7 @@ module Hobo
       ensure_directories
       ensure_files
       parsed = yield(CONFIG.keys.first)
-      Hobo.set_config!(parsed)
+      Hobo.config!(parsed)
     end
   end
 end

test/hobo/config_test.rb

@@ -5,7 +5,7 @@ class ConfigTest < Test::Unit::TestCase
   context "Hobo configuration" do
     setup do
       @settings = {:a => { :b => 1}}
-      Hobo.set_config!(@settings)
+      Hobo.config!(@settings)
     end
 
     should "prevent alteration after initial creation" do
@@ -28,5 +28,16 @@ class ConfigTest < Test::Unit::TestCase
       Hobo.alterable_config[:a] = 1
       assert_not_equal Hobo.alterable_config, Hobo.config
     end
+
+    should "alter the config given a dot chain of keys" do
+      Hobo.set_config_value 'a.b', 2
+      assert_equal Hobo.alterable_config[:a][:b], 2
+    end
+
+    should "prevent the alteration of a non leaf setting value" do
+      assert_raise Hobo::InvalidSettingAlteration do
+        Hobo.set_config_value('a', 2)
+      end
+    end
   end
 end