Added DataMapper::Property::Lookup module.

The module provides transparent access to Property and Type classes via
a const_missing method.

lib/dm-core.rb

@@ -102,6 +102,7 @@ module ActiveSupport
 require 'dm-core/property/time'
 require 'dm-core/property/class'
 require 'dm-core/property/discriminator'
+require 'dm-core/property/lookup'
 require 'dm-core/property_set'
 
 require 'dm-core/adapters'

lib/dm-core/property/lookup.rb

@@ -0,0 +1,42 @@
+module DataMapper
+  class Property
+    module Lookup
+
+      protected
+
+      #
+      # Provides transparent access to the Properties defined in
+      # {Property}. It also provides access to the legacy {Types} namespace.
+      #
+      # @param [Symbol] name
+      #   The name of the property to lookup.
+      #
+      # @return [Property, Type]
+      #   The property with the given name.
+      #
+      # @raise [NameError]
+      #   The property could not be found.
+      #
+      # @api private
+      #
+      # @since 1.0.1
+      #
+      def const_missing(name)
+        if const = Property.find_class(name)
+          return const
+        end
+
+        # only check within DataMapper::Types, if it was loaded.
+        if DataMapper.const_defined?(:Types)
+          if DataMapper::Types.const_defined?(name)
+            type = DataMapper::Types.const_get(name)
+
+            return type if type < DataMapper::Type
+          end
+        end
+
+        super
+      end
+    end
+  end
+end

spec/semipublic/property/lookup_spec.rb

@@ -0,0 +1,26 @@
+require File.expand_path(File.join(File.dirname(__FILE__), '../..', 'spec_helper'))
+require 'dm-core/property/lookup'
+
+describe DataMapper::Property::Lookup do
+  supported_by :all do
+    before(:all) do
+      @klass = Class.new { extend DataMapper::Model }
+
+      DataMapper::Types::LegacyType = Class.new(DataMapper::Types::Text)
+    end
+
+    it "should provide access to Property classes" do
+      @klass::Serial.should == DataMapper::Property::Serial
+    end
+
+    it "should provide access to legacy Types" do
+      @klass::LegacyType.should be(DataMapper::Types::LegacyType)
+    end
+
+    it "should not provide access to unknown Property classes" do
+      lambda {
+        @klass::Bla
+      }.should raise_error(NameError)
+    end
+  end
+end