Advanced Rails - Building Industrial-Strength Web Apps in Record Time

Metaprogramming Techniques | 35

module ActiveMerchant

module Billing

module Integrations

module ActionViewHelper

def payment_service_for(order, account, options = {}, &proc)

...

end

end

end

end

end

Then, in the plugin’sinit.rb script, the module is included inActionView::Base:

require 'active_merchant/billing/integrations/action_view_helper'

ActionView::Base.send(:include,

ActiveMerchant::Billing::Integrations::ActionViewHelper)

It certainly would be simpler in code to directly openActionView::Baseand add the
method, but this has the advantage of modularity. All Active Merchant code is con-
tained within theActiveMerchant module.

There is one caveat to this approach. Because any included modules are searched for
methods after the class’s own methods are searched, you cannot directly overwrite a
class’s methods by including a module:

module M

def test_method

"Test from M"

end

end

class C

def test_method

"Test from C"

end

end

C.send(:include, M)

C.new.test_method # => "Test from C"

Instead, you should create a new name in the module and usealias_method_chain:

module M

def test_method_with_module

"Test from M"

end

end

class C

def test_method

"Test from C"

end

end