An easy string manipulations in Ruby with DRY-INFLECTOR!

Episode #4

by Sebastian Wilgosz

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In this episode of Hanami Mastery screencast I want to showcase a super useful little Ruby Gem, that helped me a lot in writing my own Ruby packages.

It implements classify, underscore, constantize, all within pure ruby, without rails dependencies and without any monkey-patching core Ruby classes!

It's a dry-inflector gem written by Luca Guidi, an amazing developer, co-author of Hanami Web framework and I definitely recommend following him up.

I discovered this gem by watching one of Luca's Youtube videos - and I am super glad that I've made a habit of watching other developers' videos and presentations!


While this episode covers string transformations only, if you are interested in more advanced stuff, covering hash and object transformations, check out episode #6

The problem we've faced

Recently we needed to improve in our projects the way we distribute the commands that had been triggered in the system. Whenever the command is called, it should be properly handled and the appropriate event should be published to our event store.

I don't want to talk too much about how we approached the CQRS implementation in our systems, but I'll show a little diagram here just to visualize what I'm talking about.

In the usual web application, when you send a request, it's received by a router, which recognizes the URL of the request and passes the attached parameters and headers into the proper controller action to be handled.

Route visualization in web apsRoute visualization in web aps

In other words, if you write: articles#new in Rails, or articles.new in Hanami, the passed string will be interpreted by the router, and the controller named articles will be called with an action new.

Based on the convention of naming and the file structure, the correct constant will be instantiated and a proper method called.

We needed similar functionality for our business logic.

We had a set of commands that can happen in the system, and each of them should be handled by a proper handler, that at the end of command execution should publish an event.

Command bus visualization in ruby appsCommand bus visualization in ruby apps

We wanted a CommandBus class, that registers proper handler automatically based on the given command name, following the naming convention we created.

I know it sounds pretty complex, but it all comes down to this:

class CommandBus
  def register(command_klass, handler: nil)
    handler ||= init_handler(command_klass)
    handlers[command_klass] = handler

  def call(cmd)


  attr_reader :handlers

  def initialize
    @handlers = {}

  # Initializes the handler based on command class
  # @param "String" i.e "App::Commands::CancelPayment
  # @return Instance of handler class, i.e: "App::"CommandHanlders::OnCancelPayment
  def init_handler(command_klass)
    handler_klass_str = command_klass.split("::").tap do |items|
      items[items.index('Commands')] = "CommandHandlers"
      items[-1] = "On#{items[-1]}"

    handler_klass = handler_klass_str.constantize

This is quite a simplified version of the command bus, but it's already pretty useful. It allows us to register a command, and then just call a command bus with this command. There is only one place, where the logic of figuring out what should handle my command is - and it's a command bus.

For Commands::Create it's supposed to call CommandHanndlers::OnCreate. However, this crashes, due to the usage of constantize method.

This method is not implemented in ruby, so we would either need to write it ourselves or rely on ActiveSupport's inflector class.

We didn't want that, because ActiveSupport is a set of a WHOLE LOT of features that we did not want to use in our simple gem and we didn't want to make it Rails-Specific.

We thought about implementing it on our own, but then we've found the dry-inflector - which is exactly what we needed.


dry-inflector is a simple gem that wraps several useful string transformations into a small inflector object. Because it is so small, we gladly injected that into our internal ecosystem.

Here is a short presentation of why it's so great:

  1. It's extremely small - and therefore, it's focused on one single purpose. This allows us to integrate it with any ruby app without a problem.
  2. It's configurable - as it's a standalone object, we can configure it by adding our own rules, without affecting the global String behavior, which is great, as we have full control where we want those transformations to be applied.
  3. It's thread-safe

To use it, we only need to instantiate the inflector object, and from that, we can make use of the full set of all features it provides.

For example, we can pluralize or singularize nouns, camelize strings, demodulize, and perform several other string transformations.

Here is a little snippet I've copied from the documentation, to present the basic feature of dry-inflector.

require "dry/inflector"

inflector = Dry::Inflector.new

inflector.pluralize("book")    # => "books"
inflector.singularize("books") # => "book"

inflector.camelize("dry/inflector") # => "Dry::Inflector"
inflector.classify("books")         # => "Book"
inflector.tableize("Book")          # => "books"

inflector.dasherize("dry_inflector")  # => "dry-inflector"
inflector.underscore("dry-inflector") # => "dry_inflector"

inflector.demodulize("Dry::Inflector") # => "Inflector"

inflector.humanize("dry_inflector")    # => "Dry inflector"
inflector.humanize("author_id")        # => "Author"

inflector.ordinalize(1)  # => "1st"
inflector.ordinalize(2)  # => "2nd"
inflector.ordinalize(3)  # => "3rd"
inflector.ordinalize(10) # => "10th"
inflector.ordinalize(23) # => "23rd"

There is also the one we've looked for, constantize!

Using constantize with dry-inflector

Let's check how constantize method behaves. I'll create a minimal set, just a plain ruby script requiring a dry-inflector and creating the inflector instance.

#!/usr/bin/env ruby

require 'dry-inflector'

inflector = Dry::Inflector.new

Then Let's create the sample class, Let's call it HanamiMastery, and put some string. Maybe Subscribe!, as I actually want to ask you for that ;).

class HanamiMastery
  def call
    p 'Subscribe!'

Then let's call the constantize, passed in the "HanamiMastery" sting as a parameter.


That is amazing! Out of the box implementation of most useful string transformations, but extracted as a single feature, ready to be used!

Solving our problem

With dry-inflector gem discovered, it was almost a no-brainer to update our CommandBus to make use of it!

require 'dry-inflector'

class CommandBus
  def initialize
    @handlers = {}
    @inflector = Dry::Inflector.new

  attr_reader :inflector

  def init_handler(command_klass)
    handler_klass = inflector.constantize(handler_klass_str)

This way, we avoided implementing the method in dozens of gems supporting our microservices ecosystem, and we've quickly realized, that other inflection transformations were also very useful in our case.

That's just great! Thanks, Open-Source geeks!

Configuring the Dry::Inflector object

I'd want to yet quickly mention the configuration feature, as this is one more super-useful functionalities that dry-inflector provides. For example, I always hate, when I want to have API namespace, and I need to name classes, like: Api, or Http instead of HTTP and API for Rails to properly transform those strings. This is easily solved by Dry::Inflector by allowing to mark certain words as acronyms.

require "dry/inflector"

inflector = Dry::Inflector.new do |inflections|
  inflections.acronym "API", "JSON"

inflector.underscore("JSONAPIresponse") # => "json_api_response"
inflector.camelize("json_api_request") # => "JSONAPIResponse"

The other nice thing is that you can add your own inflections, mark certain words as uncountable, or deliver additional rules to the pluralization of certain words.

require "dry/inflector"

inflector = Dry::Inflector.new do |inflections|
  inflections.plural      "HTTP",   "Hypertext Transfer Protocols" # specify a rule for #pluralize
  inflections.uncountable "HanamiMastery"      # add an exception for an uncountable word

inflector.pluralize("HTTP")     # => "Hypertext Transfer Protocols"
inflector.pluralize("dry-inflector") # => "dry-inflector"

That's all I have for today, check out the gem's documentation if you seek more examples of usage.

Do you like this episode? Consider sponsoring the project!

I hope you've enjoyed this episode, and if you want to see more content in this fashion, Subscribe to my channel and follow me on twitter! As always, all links you can find the description of the video or in the Hanami Mastery about page

See you!

Special Thanks!

I'd like to thank All the amazing people who decided to sponsor me so far. I appreciate your trust, as I understand that too many blogs do not even hit the barrier of 10 articles!

Any support allows me to spend more time on creating content that promotes great open source projects. I hope to do more of this stuff in the future!

Do you know great Ruby gems?

Add your suggestion to our discussion panel!

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