LazyLoad

Autoload with custom callbacks

Tested and working on: 1.8.7, 1.9.2, jruby 1.5.2, rubinius 1.0.1

LazyLoad is a slightly more elaborate alternative to autoload. It helps deal with "soft" dependencies, where dependencies are "preferred", rather than strictly needed. It is very simple, but provides:

Custom callbacks
"Best available" dependency selection
A simple, optional wrapper mechanism

Unlike autoload, LazyLoad is scoped. This means that when you register a callback for the Foo constant, referencing LazyLoad::Foo will trigger the callback. Simply referencing Foo will not trigger the callback. In other words, internals are not monkey patched. However, you can also use it as a mixin, thereby eliminating the verbosity.

Samples

  
  gem install lazy_load`

  # same as as autoload:

  LazyLoad.const(:Tilt, 'tilt')

  # or the equivalent with a callback:

  LazyLoad.const(:Tilt) do
    require 'tilt'
    Tilt
  end

  # lets you..

  LazyLoad::Tilt # => Tilt (or LoadError)

  LazyLoad::Oboe
  # => NameError: uninitialized constant LazyLoad::Oboe

Note that the return value of the callback becomes the constant. Any object can be returneed.

Best available

You can use the best method to return the first constant for which the callback does not raise a LoadError, or else raise the LoadError of the first (most preferred) constant:

    LazyLoad.best(:Kramdown, :RDiscount, :Redcarpet)

    # or using named groups:

    LazyLoad.group(:markdown, :Kramdown, :RDiscount, :Redcarpet)
    LazyLoad.best(:markdown)

Mixin

You can endow objects with the LazyLoad methods by extending the LazyLoad::Mixin. Each object will have its own scope of callbacks.

  module WidgetFactoryFactory

    extend LazyLoad::Mixin

    const :Haml, 'haml'

    Haml # => Haml

  end

Wrappers

LazyLoad has super simple wrapper support, which lets you quickly define wrapper classes that are automatically wrapped around their corresponding constants. These wrappers get a default initialize method, which sets @wrapped to the object they wrap, and are set to forward method calls there using method_missing.

  LazyLoad.wrapper(:RDiscount) do

    def new(*args)
      InstanceWrapper.new(super(*args))
    end

    class InstanceWrapper < LazyLoad::Wrapper

      def render(*args); to_html(*args); end

      def go_shopping
        puts 'sure, why not'
      end

    end

  end

Feedback and suggestions are welcome through Github.