RubyContracts

RubyContracts is a small DSL to add pre & post condition to methods. It tries to bring some design by contract in the Ruby world.

Installation

Add this line to your application's Gemfile:

gem 'ruby_contracts'

And then execute:

$ bundle

Or install it yourself as:

$ gem install ruby_contracts

Usage

class Example
  include Contracts::DSL
  
  def initialize(val)
    @value = val
  end
  
  type :in => [Integer, Proc], :out => Numeric
  pre  "a must be > the example's value" do |a| a < @value end
  post "result must be between a and val" do |result, a| result >= a && result < @value end
  
  def method(a)
    a * 3 + yield - 4
  end
end

Run this sample with ENABLE_ASSERTION=1 bundle exec ruby example.rb.

Without the environment variable ENABLE_ASSERTION you have zero overhead and zero verification.

Class inheritance

When you inherit a class that contains contracts, all contracts must be satified by the subclass.

If you override a method, you still have to satisfy the existing postconditions for this method and you can add some others. This means that postconditions groups are AND-ed and preconditions groups are OR-ed by inheritance.

See the issue #1 for an example.

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Added some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request