choose_class

Facilitates choosing a class based on the value that would be passed to that class. Useful for implementing the factory method pattern.

Add this line to your application's Gemfile:

gem 'choose_class'

And then execute:

$ bundle

Or install it yourself as:

$ gem install choose_class

Include ChooseClass::Base into your base class. It will gain a choose_class method. Call choose_class and pass it a value by which to decide which class to return.

Say we're implementing an object serializer of some sort. We may have a base class that implments some common functionalty, and then several subclasses that specialise the serialization for specific types.

We want to determine which class to use based on the object we are to serialize.

module Serializers
  class Base
    include ChooseClass::Base
  end

  # Specialisation class for Fixnum values
  class Fixnum < Base
  end
end

elsewhere:

  Serializers.choose_class(1) # => Serializers::Fixnum

The class chosen was Serializers::Fixnum because it is a class in the same namespace as the base class, and it has the same name as the class of the value passed in. (These conventions are configurable in a limited way. See spec/example)

Serializers.choose_class("some string") # => Serializers::Base

The class chosen was Serializers::Base because there was no Serializers::String class to choose instead.

To complete the serializer example, a final implementation might look something like this:

module Serializers
  class Base
    include ChooseClass::Base

    def self.serialize value
      choose_class(value).new(value).serialize
    end

    def serialize
      # general object serialization implementation
    end
  end

  # Specialisation class for Fixnum values
  class Fixnum < Base
    def serialize
      # fixnum-specific serialization implementation
    end
  end
end

Serializers.serialize(1) # => output of Serializers::Fixnum.serialize
Serializers.serialize("some string") # => output of Serializers::Base.serialize

See also spec/example.