idempotent alias_method_chain

.gitignore

.bundle
.rbenv-version
zz_gems
bin

README.md

Jay Fields discusses the 'stack level too deep' problem with alias_method and alias_method_chain if a file gets loaded twice (which is not uncommon in a large enough project). This is an attempt to workaround it.

bundle install
bundle exec ruby runner.rb

You can see the simple check for instance_methods.include? on the alias_method_chain for execute prevents the chaining from happening multiple times which causes the stack level too deep.

base.rb

Bundler.require

class Base
  def execute
    puts 'base execute'
  end

  def fail
    puts 'base fail'
  end
end

extension.rb

require 'active_support/core_ext/module'

class Base
  def execute_with_awesome
    execute_without_awesome
    puts '...now with awesome!'
  end

  def fail_with_awesome
    fail_without_awesome
    puts '...now with awesome!'
  end

  alias_method_chain :execute, :awesome unless instance_methods.include? :execute_without_awesome
  alias_method_chain :fail, :awesome
end

Gemfile

source :rubygems

gem 'activesupport'

Gemfile.lock

GEM
  remote: http://rubygems.org/
  specs:
    activesupport (3.0.0)

PLATFORMS
  ruby

DEPENDENCIES
  activesupport

runner.rb

require File.dirname(__FILE__) + '/base'

# load twice to enable 'stack level too deep problem'
load File.dirname(__FILE__) + '/extension.rb'
load File.dirname(__FILE__) + '/extension.rb'

base = Base.new
base.execute
base.fail

1.8 stores method names in instance_methods as strings, not symbols.

private and protected methods won't show in instance_methods ... so ... may need to use those variants.