Gem Version

Provides a mixin and decorator to add a Hash#fetch like interface to any object.

You must define a [] subscript method for raw access to the fetchable data.

Your [] method must return anything but nil in order for #fetch to consider a key successfully fetched. False is considered sucessful.

Hash#Fetch is one of my favourite Ruby methods and can be tricky to implement its full behaviour so here it is extracted for you to add to whichever object you choose.

If you're not familiar with Hash#fetch it's a great way to help eliminate nils as it raises an error when the desired key is not found. For more info consult Ruby Hash documentation.


Add this line to your application's Gemfile:

gem 'fetchable'

And then execute:

$ bundle

Or install it yourself as:

$ gem install fetchable


Include into a object with a [] method

require "fetchable"

things = %w(zero one two).extend(Fetchable)

 => "zero"

 => "two"

 => KeyError: key not found 3

things.fetch(3, "three")
 => "three"

things.fetch(3) { "Execute a block!" }
 => "Execute a block!"

things.fetch(3) { |key| "Do something based on missing key #{key}" }
 => "Do something based on missing key 3"

Prefer composition over inheritance?

We got you covered! Use Fetchable::Decorator instead.

require "fetchable/decorator"

things = %w(zero one two)

fetchable_things = Fetchable::Decorator.new(things)

 => "one"

For bonus points use lambdas

Lambdas, procs and method objects can also be called with #[].

Why not make them fetchable?

It might be funny.

Dammit method, you better not return me a nil, I'll be so mad.


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