MethodObject

TL; DR

The method object pattern implies that you have one Ruby class for one single thing you want to perform.

This gem helps you to do just that with minimal overhead. The convention is to use the .call class method like so:

class SaySometing
  include MethodObject

  # Input
  option :text

  # Output
  def call
    puts text
  end
end

SaySometihng.call(text: 'Hi there!') # => 'Hi there!'

Rationale

A minimal implementation of the method object pattern would probably look like this. This is sometimes also referred to as "service class".

class SaySometing
  def self.call(*args, &block)
    new.call(*args, &block)
  end

  def call(text)
    puts text
  end
end

Fun fact: previously that was actually the implementation of this gem.

Basically everything passed to MyClass.call(...) would be passed on to MyClass.new.call(...).

Even better still, it should be passed on to MyClass.new(...).call so that your implementation becomes cleaner:

class SaySometing
  def self.call(*args, &block)
    new(*args, &block).call
  end

  def initialize(text:)
    @text = text
  end

  def call
    puts @text
  end
end

People implemented that, but in doing so reinvented the wheel. Because now you not only have the method object pattern (i.e. call), now you also have to deal with initialization (i.e. new).

That's where the popular dry-initializer gem comes in. It is a battle-tested way to initialize objects with mandatory and optional attributes.

The method_object gem (you're looking at it right now), combines both the method object pattern and dry initialization.

Installation

# Add this to your Gemfile
gem 'method_object`

Usage

If you only have one mandatory, obvious argument, this is what your implementation most likely would look like:

class CalculateTax
  include MethodObject

  param :product

  def call
    product.price * 0.1
  end
end

bike = Bike.new(price: 50)
CalculateTax.call(bike) # => 5

If you prefer to use named keywords, use this instead:

class CalculateTax
  include MethodObject

  option :product

  def call
    product.price * 0.1
  end
end

bike = Bike.new(price: 50)
CalculateTax.call(product: bike) # => 5

You can also use both params and options. They are all mandatory.

class CalculateTax
  include MethodObject

  param :product
  option :dutyfree

  def call
    return 0 if dutyfree
    product.price * 0.1
  end
end

bike = Bike.new(price: 50)
CalculateTax.call(bike, dutyfree: true) # => 0

You can make options optional by defining a default value in a proc:

class CalculateTax
  include MethodObject

  param :product
  option :dutyfree, default: -> { false }

  def call
    return 0 if dutyfree
    product.price * 0.1
  end
end

bike = Bike.new(price: 50)
CalculateTax.call(bike) # => 5

That's it!

Caveats

• params cannot be optional (or have default values). This is because there can be several params in a row, which leads to confusion when they are optional.

Thanks

• A big thank you to Jared who was so kind to give us the method_object gem name for our implementation.
• The dry-rb team for their sense of beauty.

License

MIT License, see LICENSE.md