LazyLoadAttributes

Simple "Ruby core"-inspired syntactic sugar for defining cached, lazy-loaded attributes which intuitively handle inheritence and attribute redefinition.

Installation

Add this line to your application's Gemfile:

gem 'lazy_load_attributes'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install lazy_load_attributes

Usage

The class-level lazy_attr_reader method defines a lazy-loaded attribute.

A simple use-case:

require "lazy_load_attributes"

class Example
  extend LazyLoadAttributes

  lazy_attr_reader(:lazy_attr) { puts "loaded"; lazy_attr_method }

  def lazy_attr_method
    "lazy value"
  end
end

example = Example.new
example.lazy_attr
# loaded
# => "lazy value"
example.lazy_attr
# => "lazy value"

This illustrates four major powers of LazyLoadAttributes:

• the attribute calls evaluate and return their definition's initializer
• the initializer is not evaluated until the first attribute call
• the initializer is evaluated in the context of the calling instance (i.e. example in the sample above), so its instance methods are available during evaluation as they would be within the body of a normal instance method
• the initializer is evaluated only once; subsequent attribute calls are served from a cache

Inheritence is handled transparently:

class Superclass
  extend LazyLoadAttributes

  lazy_attr_reader(:super_attr) { super_attr_value }
  lazy_attr_reader(:redefine_attr) { "redefine_attr from Superclass" }

  def super_attr_value
    "Superclass#super_attr_value"
  end

  def sub_attr_value
    "Superclass#sub_attr_value"
  end
end

class Subclass < Superclass
  lazy_attr_reader(:redefine_attr) { "redefine_attr from Subclass" }
  lazy_attr_reader(:sub_attr) { sub_attr_value }

  def super_attr_value
    "Subclass#super_attr_value"
  end
end

super_instance = Superclass.new
super_instance.super_attr
# => "Superclass#super_attr_value"
super_instance.redefine_attr
# => "redefine_attr from Superclass"

sub_instance = Subclass.new
sub_instance.super_attr
# => "Subclass#super_attr_value"
sub_instance.sub_attr
# => "Superclass#sub_attr_value"
sub_instance.redefine_attr
# => "redefine_attr from Subclass"

The call to sub_instance.super_attr shows that the instance methods used by an initializer respect inheritence even when the attribute itself is defined in the superclass

The call to sub_instance.sub_attr shows that initializers used by definitions in a subclass have access to instance methods defined in a superclass

The call to sub_instance.redefine_attr shows that an attribute redefined in a subclass will override its definition in the superclass

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec 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. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and the created tag, and push the .gem file to rubygems.org.

Contributing

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

License

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

Code of Conduct

Everyone interacting in the LazyLoadAttributes project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.