Oct 10, 2015

Making Bottomless Hash Ruby Gem

After creating Bottomless Hash last time and writing tests the next logical step is to make a Gem out of it.


First things first. Let's see if the name is not taken.

$ gem search bottomless_hash


Looks good, now generate a template and an empty git repo to have less typing. We'll use RSpec, since I already have tests written.

$ bundle help gem                                                                                                                                                            127 ↵
  bundle gem GEM [OPTIONS]

  -b, [--bin], [--no-bin]            # Generate a binary for your library.
      [--coc], [--no-coc]            # Generate a code of conduct file. Set a default with `bundle config gem.coc true`.
  -e, [--edit=EDITOR]                # Open generated gemspec in the specified editor (defaults to $EDITOR or $BUNDLER_EDITOR)
      [--ext], [--no-ext]            # Generate the boilerplate for C extension code
      [--mit], [--no-mit]            # Generate an MIT license file. Set a default with `bundle config gem.mit true`.
  -t, [--test=rspec]                 # Generate a test directory for your library, either rspec or minitest. Set a default with `bundle config gem.test rspec`.
      [--no-color], [--no-no-color]  # Disable colorization in output
  -r, [--retry=NUM]                  # Specify the number of times you wish to attempt network commands
  -V, [--verbose], [--no-verbose]    # Enable verbose output mode

Create a Ruby Gem skeleton with RSpec as a test runner.

$ bundle gem bottomless_hash -t=rspec
Creating gem 'bottomless_hash'...
Do you want to include a code of conduct in gems you generate?
Codes of conduct can increase contributions to your project by contributors who prefer collaborative, safe spaces. You can read more about the code of conduct at contributor-covenant.org. Having a code of conduct means agreeing to the responsibility of enforcing it, so be sure that you are prepared to do that. For suggestions about how to enforce codes of conduct, see bit.ly/coc-enforcement. y/(n): y
Code of conduct enabled in config
Do you want to license your code permissively under the MIT license?
This means that any other developer or company will be legally allowed to use your code for free as long as they admit you created it. You can read more about the MIT license at choosealicense.com/licenses/mit. y/(n): y
MIT License enabled in config
      create  bottomless_hash/Gemfile
      create  bottomless_hash/.gitignore
      create  bottomless_hash/lib/bottomless_hash.rb
      create  bottomless_hash/lib/bottomless_hash/version.rb
      create  bottomless_hash/bottomless_hash.gemspec
      create  bottomless_hash/Rakefile
      create  bottomless_hash/README.md
      create  bottomless_hash/bin/console
      create  bottomless_hash/bin/setup
      create  bottomless_hash/CODE_OF_CONDUCT.md
      create  bottomless_hash/LICENSE.txt
      create  bottomless_hash/.travis.yml
      create  bottomless_hash/.rspec
      create  bottomless_hash/spec/spec_helper.rb
      create  bottomless_hash/spec/bottomless_hash_spec.rb
Initializing git repo in gems/bottomless_hash

I have included all this licences and codes of conduct as some people are very sensitive to this and will email you asking if they can change your code if you won't include any of these.

Okay it is quite a handful so I'll publish it on GitHub.

$ git remote add origin [email protected]:firedev/bottomless_hash.git
$ git push -u origin master
Counting objects: 21, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (18/18), done.
Writing objects: 100% (21/21), 4.75 KiB | 0 bytes/s, done.
Total 21 (delta 0), reused 0 (delta 0)
To [email protected]:firedev/bottomless_hash.git
 * [new branch]      master -> master
 Branch master set up to track remote branch master from origin.

Great now let's get to business.

Filling up the blanks

There is a bunch of files but for now we just need to fill up bottomless_hash.gemspec.

# coding: utf-8
lib = File.expand_path('../lib', __FILE__)
$LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
require 'bottomless_hash/version'

Gem::Specification.new do |spec|
  spec.name          = "bottomless_hash"
  spec.version       = BottomlessHash::VERSION
  spec.authors       = ["Nick Ostrovsky"]
  spec.email         = ["[email protected]"]

  spec.summary       = %q{Ruby Hash modified to accept keys blindly}
  spec.description   = %q{Is there a way to blindly assign nested values to a
                          Ruby hash without creating each key’s hash separately? Yes, but it’s more
                          involved than you’d think.}
  spec.homepage      = "https://github.com/firedev/bottomless_hash"
  spec.license       = "MIT"

  # Prevent pushing this gem to RubyGems.org by setting 'allowed_push_host', or
  # delete this section to allow pushing this gem to any host.
  # if spec.respond_to?(:metadata)
  #   spec.metadata['allowed_push_host'] = "TODO: Set to 'http://mygemserver.com'"
  # else
  #   raise "RubyGems 2.0 or newer is required to protect against public gem pushes."
  # end

  spec.files         = `git ls-files -z`.split("\x0").reject { |f| f.match(%r{^(test|spec|features)/}) }
  spec.bindir        = "exe"
  spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
  spec.require_paths = ["lib"]

  spec.add_development_dependency "bundler", "~> 1.10"
  spec.add_development_dependency "rake", "~> 10.0"
  spec.add_development_dependency "rspec"

That'll do it. I just commented out the part about not letting this gem to be pushed to public repos. RSpec development dependency is already injected so I guess we are good to go.

Add the meat, not the heat

Now let us add the actual files. If you take a look Ruby gems are following the simple structure.


The file in lib is required by default, version.rb is a single constant, everything else is up to you.

The common way of structuring stuff is to put everything in the lib/gem_name and require from lib/gem_name.rb that makes everything a bit tidier. But we have nothing to hide so let's put everything from the GitHub gist into lib/bottomless_hash.rb

# lib/bottomless_hash.rb

require "bottomless_hash/version"

class BottomlessHash < Hash
  def initialize
    super &-> h, k { h[k] = self.class.new }

  def self.from_hash(hash)

class Hash
  def bottomless

And don't forget specs.

# spec/bottomless_hash
require 'spec_helper'

describe BottomlessHash do
  it 'has a version number' do
    expect(BottomlessHash::VERSION).not_to be nil

  it 'does not raise on missing key' do
    expect do
    end.to_not raise_error

  it 'returns an empty value on missing key' do
    expect(subject[:missing][:key]).to be_empty

  it 'stores and returns keys' do
    subject[:existing][:key] = :value
    expect(subject[:existing][:key]).to eq :value

  describe '#from_hash' do
    let (:hash) do
      { existing: { key: { value: :hello } } }

    subject do

    it 'returns old hash values' do
      expect(subject[:existing][:key][:value]).to eq :hello

    it 'provides a bottomless version' do
      expect(subject[:missing][:key]).to be_empty

    it 'stores and returns new values' do
      subject[:existing][:key] = :value
      expect(subject[:existing][:key]).to eq :value

    it 'converts nested hashes as well' do
      expect do
      end.to_not raise_error

Now lets run it. You will see some errors, stemming from the fact that version.rb thinks BottomlessHash is a module. We could wrap everything up in the module, but I don't have any good ideas for naming. So let's just patch the things up quickly.

# lib/bottomless_hash/version.rb

class BottomlessHash < Hash
  VERSION = "0.1.0"

A little bit ugly but okay.

$ bundle
$ rspec

  has a version number
  does not raise on missing key
  returns an empty value on missing key
  stores and returns keys
    returns old hash values
    provides a bottomless version
    stores and returns new values
    converts nested hashes as well

Finished in 0.00668 seconds (files took 0.12033 seconds to load)
8 examples, 0 failures

Okay that part went fine. Commit and push to Github. It might be a bit too verbose for the purpose of this post, but by documenting everything so I can use it later.

Let's add another test to make sure Ruby Hash class gets patched as well. This time we would have to require BottomlessHash as spec_helper would not be able to infer it's name from the spec file.

# spec/hash_spec.rb

require_relative '../lib/bottomless_hash'

describe Hash do
  subject do
      existing: {
        key: :hello
  it 'is a BottomlessHash now' do
    expect(subject).to be_a BottomlessHash

  it 'returns values for existing keys' do
    expect(subject[:existing][:key]).to eq :hello

  it 'bottomlessly stores values' do
    subject[:new][:value] = :omg
    expect(subject[:new][:value]).to eq :omg

  it 'does not raise error on missing keys' do
    expect do
    end.to_not raise_error

Another pass and we're good to go.

$ rspec spec/hash_spec.rb

  is a BottomlessHash now
  returns values for existing keys
  bottomlessly stores values
  does not raise error on missing keys

Finished in 0.00285 seconds (files took 0.09323 seconds to load)
4 examples, 0 failures

Now let's add some docs and publish.


After getting an account on RubyGems it is simple.

First you have to build a gem.

$ gem build bottomless_hash.gemspec                                                                                                    1 ↵
WARNING:  open-ended dependency on rspec (>= 0, development) is not recommended
  if rspec is semantically versioned, use:
    add_development_dependency 'rspec', '~> 0'
WARNING:  See http://guides.rubygems.org/specification-reference/ for help
  Successfully built RubyGem
  Name: bottomless_hash
  Version: 0.1.0
  File: bottomless_hash-0.1.0.gem

Okay it worked but I'd like to get rid of the warning, so I change the line in .gemspec as suggested.

$ git diff
diff --git a/bottomless_hash.gemspec b/bottomless_hash.gemspec
index b0a7bb7..817054f 100644
--- a/bottomless_hash.gemspec
+++ b/bottomless_hash.gemspec
@@ -31,5 +31,5 @@ Gem::Specification.new do |spec|

   spec.add_development_dependency "bundler", "~> 1.10"
   spec.add_development_dependency "rake", "~> 10.0"
-  spec.add_development_dependency "rspec"
+  spec.add_development_dependency "rspec", "~> 0"
$ gem build bottomless_hash.gemspec
  Successfully built RubyGem
  Name: bottomless_hash
  Version: 0.1.0
  File: bottomless_hash-0.1.0.gem

Now the gem is built without warnings. And we can push it to RubyGems.

$ gem push bottomless_hash-0.1.0.gem
Enter your RubyGems.org credentials.
Don't have an account yet? Create one at https://rubygems.org/sign_up
   Email:   [email protected]

Signed in.

Pushing gem to https://rubygems.org...
Successfully registered gem: bottomless_hash (0.1.0)

This is it. The gem is published and you can use it right away:

$ gem search bottomless_hash


bottomless_hash (0.1.0)

Bottomless Ruby Hash
Making Bottomless Hash Ruby Gem
Github firedev/bottomless_hash
Gist bottomless_hash.rb


Nick Ostrovsky

Full-stack designer. I like to keep things as minimal and as simple as possible.

Started to program with Sinclair Spectrum and has moved to user experience and interfaces since. Developed and contributed to projects for major brands such as L'Oreal, JTI and AB InBev among others. I am currently working as an independent contractor.

I live in Phuket, Thailand and enjoy the beautiful scenery with wife and two daughters.