Bundler subgroups, second approach

Gemfile

source "https://rubygems.org"

# Internal: A Hash of Procs containing subgroup code.
@subgroups = {}

# Public: Defines a subgroup for later inclusion in an environment-based group.
#
#   name  - A Symbol name for the group.
#   block - A Proc to be called when the subgroup is included.
#
# Returns nothing.
def subgroup(name, &block)
  @subgroups[name] = block
end

# Public: Includes gems in a group by evaluating stored Procs within an environment-based group.
#
#   group_name      - The Symbol name of the group to compose.
#   subgroup_names  - One or more Symbol names of the subgroup(s) to include.
#
# Returns nothing.
def compose_group(group_name, *subgroup_names)
  group(group_name) do
    subgroup_names.each { |name| @subgroups[name].call }
  end
end

### Default gems
### These gems are required in all environments.

gem "rails", "3.0.13"
gem "mysql2"

### Subgroups

subgroup :debugger do
  gem "debugger", require: nil
end

subgroup :pry do
  gem "pry"
  gem "pry-rails", require: nil
  gem "pry-nav"
  gem "pry-coolline"
  gem "pry-doc"
end

subgroup :factories do
  gem "factory_girl_rails"
end

subgroup :test_frameworks do
  gem "rspec-rails"
  gem "cucumber-rails", require: nil
  gem "capybara"
end

subgroup :test_support do
  gem "simplecov", require: nil
  gem "spork"
end

subgroup :test_doubles do
  gem "rr"
  gem "vcr"
end

subgroup :console do
  gem "wirble"
  gem "hirb"
end

### Groups
### These groups will be loaded by Bundler based on Rack environment. Each
### call to compose_group defines an environment group and the list of
### subgroups that compose it.

compose_group :development,
              :factories, :console, :debugger, :pry

compose_group :test,
              :factories, :test_frameworks, :test_support, :test_doubles,
              :debugger, :pry