RConditions

RConditions generates a bang method (for example, Array#empty!) for each predicate method (for example, Array#empty?). The bang method will pass if the predicate method passes, otherwise it will throw an exception. The exception will include auto-generated modules that give information which predicate methods passed or failed in the bang method‘s execution.

Download

RConditions is hosted on RubyForge, and published as a gem. Installation is straightforward:

Install RubyGems
gem install rconditions

You may also download the gem on RConditions's RubyForge project page.

Example

  require "rconditions"

  class Posting
    attr_writer :spam, :active

    def spam?
      @spam
    end

    def active?
      @active
    end

    def visible?
      !spam? && active?
    end
  end

  class User
    attr_writer :admin

    def admin?
      @admin
    end

    def can_view_posting?(posting)
       admin? || posting.visible?
    end
  end

  user = User.new
  user.admin = false

  posting = Posting.new
  posting.active = false
  posting.spam = true

  begin
    user.can_view_posting!(posting)
  rescue Posting::SpamError => e
    p e
  rescue Posting::NotActiveError
    puts "should not get here"
  end

  # => #<Exception: User::NotAdminError, Posting::SpamError,
  #      Posting::NotVisibleError, User::NotCanViewPostingError>

As you can see, the raised exception includes modules for each of the evaluated predicate methods: User#can_view_posting!(posting) in the context above called User#can_view_posting?(posting), which called User#admin? and Posting#visible?, which called Posting#spam?.

The results were

User#admin? # => false
Posting#spam? # => true
Posting#visible? # => false
User#can_view_posting? # => false

The names of the included exception modules are derived from the names of the predicate methods:

User::NotAdminError
Posting::SpamError
Posting::NotVisibleError
User::NotCanViewPostingError

Performance

As almost all predicate methods are extended by default, RConditions carries a performance penalty which varies with the number of calls to predicate methods. A simple test setup using mongrel/rails was slowed down by more than 30% by adding require "rconditions" to the bottom of its enviroment.rb.

The performance penalty can be avoided by applying RConditions only to new methods, that is, methods defined after require "rconditions". To achieve this, set ::RCONDITIONS_ONLY_FOR_NEW_METHODS = true before the require call. Our test setup had no measurable slowdown afterwards.

Supported Ruby Versions

The test suite of RConditions passes for

ruby 1.8.6
ruby 1.9.0 (tested with revision 13680)
jruby 1.1 (tested with revision 4574)

If you use another ruby version, please check whether the tests pass.

Limitations

RConditions only processes predicate methods starting with a letter and containing only word characters except the question mark at the end.
Kernel#block_given? is not processed.
Singleton methods on classes and modules are not processed.

License

RConditions is released under the MIT license.

Authors

RConditions is written by Norman Timmler and Tammo Freese.

README