File: README — Documentation for to

Treat an array of objects and a singular object uniformly as a collection of objects.

Especially useful in processing REST Web Service API JSON responses in a uniform functional approach.

ToCollection is a Ruby Refinement, so it may be safely enabled via using ToCollection where needed only.

Introduction

Canonicalize data to treat uniformly whether it comes in as a single object or an array of objects, dropping nils out automatically.

API: object#to_collection(compact=true) where compact is a boolean for whether to compact collection or not. It is true by default.

Example:

city_counts = {}
people_http_request.to_collection.each do |person|
  city_counts[person["city"]] ||= 0
  city_counts[person["city"]] += 1
end

Wanna keep nil values? No problem! Just pass false as an argument:

bad_people_count = 0
city_counts = {}
people_http_request.to_collection(false).each do |person|
  if person.nil?
    bad_people_count += 1
  else
    city_counts[person["city"]] ||= 0
    city_counts[person["city"]] += 1
  end
end

Instructions

Bundler

Add gem 'to_collection', '~> 2.0.0' to Gemfile
Run bundle
Require to_collection ruby gem in code (e.g. via Bundler.require(:default) or require 'bundler/setup' & require 'to_collection')
Add using ToCollection to the top of the Ruby file you would like to refine Object in with #to_collection method.

Manual Gem Install

Run gem install to_collection -v2.0.0
Add require 'to_collection' to code
Add using ToCollection to the top of the Ruby file you would like to refine Object in with #to_collection method.

Note

If '#to_collection' was already defined on Object in a project, requiring the to_collection library will print a warning.

It is still safe to require as it does not overwrite Object#to_collection except in Ruby files where using ToCollection is added.

Background

I'm sure you've encountered REST Web Service APIs that operate as follows:

HTTP Request: =>

GET /people

<= 1 person JSON Response:

{"first_name":"John","last_name":"Barber","city":"Chicago"}

HTTP Request: =>

GET /people

<= 3 people JSON Response:

[{"first_name":"John","last_name":"Barber","city":"Chicago"}, {"first_name":"Mark","last_name":"Jones","city":"New York"}, {"first_name":"Josh","last_name":"Beeswax","city":"Denver"}]

How do you work with the varied JSON responses in Ruby?

One approach for an app that needs to count people in cities:

city_counts = {}
json_response = people_http_request
if json_response.is_a?(Hash)
  city_counts[json_response["city"]] ||= 0
  city_counts[json_response["city"] += 1
elsif json_response.is_a?(Array)
  json_response.each do |person|
    city_counts[person["city"]] ||= 0
    city_counts[person["city"]] += 1
  end
end

Not only is the code above repetitive (unDRY) and complicated, but it also breaks common Ruby and object oriented development standards by relying on explicit type checking instead of duck-typing, polymorphism, or design patterns.

A slightly better version relying on duck-typing would be:

city_counts = {}
json_response = people_http_request
if json_response.respond_to?(:each_pair)
  city_counts[json_response["city"]] ||= 0
  city_counts[json_response["city"] += 1
elsif json_response.respond_to?(:each_index)
  json_response.each do |person|
    city_counts[person["city"]] ||= 0
    city_counts[person["city"]] += 1
  end
end

A slightly clearer version relying on design patterns (Strategy) and parametric polymorphism (functional) would be:

city_counts = {}
city_counting_strategies = {
  Hash: -> { |json_response|
    city_counts[json_response["city"]] ||= 0
    city_counts[json_response["city"] += 1
  },
  Array: -> { |json_response|
    json_response.each do |person|
      city_counts[person["city"]] ||= 0
      city_counts[person["city"]] += 1
    end
  }
}
json_response = people_http_request
city_counting_strategies[json_response.class].call(json_response)

A more radical version relying on object-oriented polymorphism and Ruby open-classes would be:

Hash.class_eval do
  def process_json_response(&processor)
    processor.call(self)
  end
end

Array.class_eval do
  def process_json_response(&processor)
    each(&processor)
  end
end

city_counts = {}
json_response = people_http_request
json_response.process_json_response do |person|
  city_counts[person["city"]] ||= 0
  city_counts[person["city"]] += 1
end

This version is quite elegant, clear, and Ruby idiomatic, but aren't we using a Nuclear device against a fly that sometimes comes as a swarm of flies? I'm sure we can have a much simpler solution, especially in a language like Ruby.

Well, how about this functional solution?

city_counts = {}
[people_http_request].flatten.each do |person|
  city_counts[person["city"]] ||= 0
  city_counts[person["city"]] += 1
end

Yes, hybrid functional/object-oriented programming to the rescue.

One may wonder what to do if the response comes in as nil or includes nil values in an array. Well, this approach can scale to handle that too should ignoring nil be the requirement.

city_counts = {}
[people_http_request].flatten.compact.each do |person|
  city_counts[person["city"]] ||= 0
  city_counts[person["city"]] += 1
end

Can we generalize this elegant solution beyond counting cities? After all, the key problem with the code on top is it gets quite expensive to maintain in a real-world production app containing many integrations with REST Web Service APIs.

This functional generalization should work by allowing you to switch json_response variable and process_json_response proc anyway you want:

[json_response].flatten.compact.each(&:process_json_response)

Example:

[cities_json_response].flatten.compact.each(&:group_by_country)

How about go one step further and bake this into all objects using our previous approach of object-oriented polymorphism and Ruby open-classes? That way, we don't just collapse the difference between dealing with arrays of hashes vs hashes but also arrays of objects vs singular objects by adding. Note the use of flatten(1) below to prevent arrays or arrays from collapsing more than one level.

class Object
  def to_collection
    [self].flatten(1).compact
  end
end

Example usage (notice how more readable this is than the explicit version above by hiding flatten and compact):

city_counts = {}
people_http_request.to_collection.each do |person|
  city_counts[person["city"]] ||= 0
  city_counts[person["city"]] += 1
end

A refactored version including optional compacting would be:

class Object
  def to_collection(compact=true)
    collection = [self].flatten(1)
    compact ? collection.compact : collection
  end
end

Example usage of to_collection(compact) to count bad person hashes coming as nil:

bad_people_count = 0
city_counts = {}
people_http_request.to_collection(false).each do |person|
  if person.nil?
    bad_people_count += 1
  else
    city_counts[person["city"]] ||= 0
    city_counts[person["city"]] += 1
  end
end

Of course, in Ruby 2+, you may use Ruby Refinements, so simply include Object#to_collection via this line instead:

using ToCollection

You asked for "Elegant" didn't you? I hope that was what you were looking for.

How It Works

A Ruby Refinement is activated via using ToCollection adding/overwriting the #to_collection method in Object, which is the ancestor of all Ruby objects.

Release Notes

v2.0.0

Revamped API using Ruby Refinements (safer than monkey-patching)
Removed super_module gem dependency
Dropped safety options since Ruby Refinements already handle things safely

v1.0.1

Updated super_module gem version to relax indirect method_source gem version dependency

Contributing

Check out the latest master to make sure the feature hasn't been implemented or the bug hasn't been fixed yet.
Check out the issue tracker to make sure someone already hasn't requested it and/or contributed it.
Fork the project.
Start a feature/bugfix branch.
gem install bundler
bundle
Commit and push until you are happy with your contribution.
Make sure to add tests for it. This is important so I don't break it in a future version unintentionally. Also, do not upgrade jeweler. It is intentionally at an old version that is compatible with running tests in Travis with older verison of Ruby as well as supporting Coveralls, Simplecov, and Code Climate.
Please try not to mess with the Rakefile, version, or history. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate to its own commit so I can cherry-pick around it.

ToCollection 2.0.0 Ruby Refinement