The code and tests for the "Deep Fetch" by Dan Reedy

hash_deep_fetch.rb

#!/usr/bin/env ruby

require 'minitest/autorun'

Hash.class_eval do
  def deep_fetch(*keys, default: nil)
    keys.reduce(self) do |memo, key|
      memo.fetch(key)
    end
  rescue KeyError
    default.nil? ? raise : default
  end

  def fetch_keypath(keypath, default: nil)
    deep_fetch(*keypath.split('.'), default: default)
  end
end

describe Hash do
  before do
    @hash = {
      "webserver" => {
        "users" => {
          "admin" => {
            "password" => "some amazing password"
          }
        }
      }
    }
  end

  describe '#deep_fetch' do
    it 'returns the correct value for the provided keys' do
      @hash.deep_fetch('webserver','users','admin','password').must_equal 'some amazing password'
    end
    it 'raises KeyError if the provided keys do not exist' do
      -> { @hash.deep_fetch('webserver','users','jdoe','password') }.must_raise KeyError
    end
    it 'returns the provided default value if the key does not exist' do
      @hash.deep_fetch('webserver','users','jdoe','password', default: 'Key Missing').must_equal 'Key Missing'
    end
    it 'returns the provided default value if the key does not exist' do
      @hash.deep_fetch('webserver','users','jdoe','password', default: false).must_equal false
    end
  end
  describe '#fetch_keypath' do
    it 'returns the correct value for the provided keypath' do
      @hash.fetch_keypath('webserver.users.admin.password').must_equal 'some amazing password'
    end
    it 'raises KeyError if the provided keys do not exist' do
      -> { @hash.fetch_keypath('webserver.users.jdoe.password') }.must_raise KeyError
    end
    it 'returns the provided default value if the key does not exist' do
      @hash.fetch_keypath('webserver.users.jdoe.password', default: 'Key Missing').must_equal 'Key Missing'
    end
  end
end