Smart Init - Simple service objects in Ruby

Do you find yourself writing a lot of boilerplate code like this?

def initialize(network_provider, api_token)
  @network_provider = network_provider
  @api_token = api_token
end

def self.call(network_provider, api_token)
  new(network_provider, api_token).call
end

This gem provides a simple DSL for getting rid of it. It offers an alternative to using Struct.new which does not check for number of parameters provided in initializer, exposes getters and instantiates unecessary class instances.

Smart Init offers a unified API convention for stateless service objects, accepting values in initializer and exposing one public class method call which instantiates new objects and accepts arguments passed to initializer.

Check out this blog post for my reasoning behind this approach to service object pattern.

Installation

In your Gemfile

gem 'smart_init'

API

You can use it either by extending a module:

require 'smart_init'

class ApiClient
  extend SmartInit

  initialize_with :network_provider, :api_token
end

or subclassing:

class ApiClient < SmartInit::Base
  initialize_with :network_provider, :api_token
end

Now you can just:

object = ApiClient.new(network_provider: Faraday.new, api_token: 'secret_token')
# <ApiClient:0x007fa16684ec20 @network_provider=Faraday<...>, @api_token="secret_token">

If you omit a required attribute an ArgumentError will be thrown:

client = ApiClient.new(network_provider: Faraday.new)

# ArgumentError (missing required attribute api_token)

Making the object callable

You can use the is_callable method:

class Calculator < SmartInit::Base
  initialize_with :data
  is_callable

  def call
    ...
    result
  end
end

Calculator.call(data: data) => result

Optionally you can customize a callable method name:

class Routine < SmartInit::Base
  initialize_with :params
  is_callable method_name: :run!

  def run!
    ...
  end
end

Routine.run!(params: params)

Default arguments

You can use hash based, default argument values:

class Adder < SmartInit::Base
  initialize_with :num_a, num_b: 2
  is_callable

  def call
    num_a + num_b
  end
end

Adder.call(num_a: 2) => 4
Adder.call(num_a: 2, num_b: 3) => 5

Readers access

Contrary to using Struct, by default the reader methods are not publicly exposed:

client = ApiClient.new(network_provider: Faraday.new, api_token: 'secret_token')
client.api_token => # NoMethodError (private method `api_token' called for #<ApiClient:0x000..>)

Optionally you can make all or subset of readers public using the public_readers config option. It accepts true or an array of method names as an argument.

class PublicApiClient < SmartInit::Base
  initialize_with :network_provider, :api_token, public_readers: true
end

client = PublicApiClient.new(network_provider: Faraday.new, api_token: 'secret_token')
client.network_provider => #<Faraday::Connection:0x000...>
client.api_token => 'secret_token'

class SemiPublicApiClient < SmartInit::Base
  initialize_with :network_provider, :api_token, public_readers: [:network_provider]
end

client = SemiPublicApiClient.new(network_provider: Faraday.new, api_token: 'secret_token')
client.network_provider => #<Faraday::Connection:0x000...>
client.api_token => 'secret_token' => # NoMethodError (private method `api_token' called for #<SemiPublicApiClient:0x000...>)

Accessors access

Similarly, this is how it would look if you tried to use a writer method:

client = ApiClient.new(network_provider: Faraday.new, api_token: 'secret_token')
client.api_token = 'new_token' => # NoMethodError (private method `api_token=' called for #<ApiClient:0x000..>)

Optionally you can make all or subset of accessors public using the public_accessors config option. It accepts true or an array of method names as an argument. This will provide both reader and writer methods publicly.

class PublicApiClient < SmartInit::Base
  initialize_with :network_provider, :api_token, public_accessors: true
end

client = PublicApiClient.new(network_provider: Faraday.new, api_token: 'secret_token')
client.network_provider => #<Faraday::Connection:0x000...>
client.network_provider = Typhoeus::Request.new(...) => #<Typhoeus::Request:0x000...>
client.api_token => 'secret_token'
client.api_token = 'new_token' => 'new_token'

class SemiPublicApiClient < SmartInit::Base
  initialize_with :network_provider, :api_token, public_accessors: [:network_provider]
end

client = SemiPublicApiClient.new(network_provider: Faraday.new, api_token: 'secret_token')
client.network_provider => #<Faraday::Connection:0x000...>
client.network_provider = Typhoeus::Request.new(...) => #<Typhoeus::Request:0x000...>
client.api_token => # NoMethodError (private method `api_token' called for #<SemiPublicApiClient:0x000...>)
client.api_token = 'new_token' => # NoMethodError (undefined method `api_token=' called for #<SemiPublicApiClient:0x000...>)

Finally, you can mix them together like this:

class PublicReadersSemiPublicAccessorsApiClient < SmartInit::Base
  initialize_with :network_provider, :api_token, :timeout,
                  public_readers: true, public_accessors: [:network_provider]
end

client = PublicReadersSemiPublicAccessorsApiClient.new(
           network_provider: Faraday.new, api_token: 'secret_token', timeout_length: 100
         )
client.network_provider => #<Faraday::Connection:0x000...>
client.network_provider = Typhoeus::Request.new(...) => #<Typhoeus::Request:0x000...>
client.api_token => 'secret_token'
client.api_token = 'new_token' => # NoMethodError (undefined method `api_token=' called for #<SemiPublicApiClient:0x000...>)
client.timeout_length => 100
client.timeout_length = 150 => # NoMethodError (undefined method `timeout_length=' called for #<SemiPublicApiClient:0x000...>)

class SemiPublicReadersSemiPublicAccessorsApiClient < SmartInit::Base
  initialize_with :network_provider, :api_token, :timeout,
                  public_readers: [:timeout], public_accessors: [:network_provider]
end

client = SemiPublicReadersSemiPublicAccessorsApiClient.new(
           network_provider: Faraday.new, api_token: 'secret_token', timeout_length: 100
         )
client.network_provider => #<Faraday::Connection:0x000...>
client.network_provider = Typhoeus::Request.new(...) => #<Typhoeus::Request:0x000...>
client.api_token => # NoMethodError (private method `api_token' called for #<SemiPublicReadersSemiPublicAccessorsApiClient:0x000...>)
client.api_token = 'new_token' => # NoMethodError (undefined method `api_token=' called for #<SemiPublicReadersSemiPublicAccessorsApiClient:0x000...>)
client.timeout_length => 100
client.timeout_length = 150 => # NoMethodError (undefined method `timeout_length=' called for #<SemiPublicReadersSemiPublicAccessorsApiClient:0x000...>)