Logica

Logica is a reusable implementation of the Specification design pattern, or a framework to manage predicates of arbitrary complexity.

Installation

Add this line to your application’s Gemfile:

gem 'logica'

And then execute:

$ bundle

Or install it yourself as:

$ gem install logica

Usage

Here is a simple example:

class IsEven < Logica::Predicates::Base
  def satisfied_by?(number)
    number.even?
  end
end
class IsGreaterThan < Logica::Predicates::Base
  attr_reader :threshold
  def initialize(threshold)
    @threshold = threshold
  end
  def satisfied_by?(number)
    number > threshold
  end
end
is_even = IsEven.new
is_even.satisfied_by?(1)    # false
is_even.satisfied_by?(2)    # true
is_even.negated.satisfied_by?(3)    # true
is_even.negated.satisfied_by?(4)    # false
is_greater_than_five = IsGreaterThan.new(5)
is_greater_than_five.satisfied_by?(5) # false
is_greater_than_five.satisfied_by?(6) # true
is_even.and(is_greater_than_five).satisfied_by?(6) # true
is_even.and(is_greater_than_five).satisfied_by?(7) # false
is_even.or(is_greater_than_five).satisfied_by?(8) # true
is_even.or(is_greater_than_five).satisfied_by?(9) # true

More examples that show many more features can be found in the test files.

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/eugeniobruno/logica. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

The gem is available as open source under the terms of the MIT License.