Bring Environment Calculators and Environment Extension from spree_core

lib/spree/core/environment/calculators.rb

@@ -0,0 +1,12 @@
+module Spree
+  module Core
+    class Environment
+      class Calculators
+        include EnvironmentExtension
+
+        attr_accessor :shipping_methods, :tax_rates
+      end
+    end
+  end
+end
+

lib/spree/core/environment_extension.rb

@@ -0,0 +1,25 @@
+module Spree
+  module Core
+    module EnvironmentExtension
+      extend ActiveSupport::Concern
+
+      def add_class(name)
+        self.instance_variable_set "@#{name}", Set.new
+
+        create_method( "#{name}=".to_sym ) { |val|
+          instance_variable_set( "@" + name, val)
+        }
+
+        create_method(name.to_sym) do
+          instance_variable_get( "@" + name )
+        end
+      end
+
+      private
+
+        def create_method(name, &block)
+          self.class.send(:define_method, name, &block)
+        end
+    end
+  end
+end