Nilable

Nilable object is a tool to handle nil invocations.

Any nilable object wraps a single value object and proxy method invocations to it. In turn, every method result is wrapped in a nilable object.

If somewhere along the call chain, a method result is nil, no NoMethodError will be raised and you can keep on chaining method calls. It acts as a black hole object.

Installation

Add this line to your application's Gemfile:

gem 'nilable'

Usage

Nilable objects come to the rescue, when you're working on legacy code bases, where you can't avoid the nils and you have to deal with them. In fresh projects, you don't wanna use nilable objects, but avoid leaking the nils in the first place. With that out of the way, here is how you can use the nilable objects.

Imagine a legacy system where an user has an account. There are no database constraints and User#account can always be nil. In fact, it already is in old production users.

Every time you get to work with an user object and have to get its account, you have to check whether its nil. Even worse, if the account has nilable fields as well, you have to check them too:

def format_currency(user)
  if account = user.account
    if currency = account.currency
      currency.format
    end
  end
end

Forget one check and you break. Forget a test and you break in production.

In such hostile systems, you can use the nilable objects to save yourself all those checks. Wrap your hostile objects and call your methods away. If a nil happens anywhere in the call chain, another nilable object will be returned. When done, call Nilable#value to extract the value out of the nilable object.

def format_currency(user)
  Nilable(user.account).currency.format.value
end

That's it. Wrap your hostile objects in nilable and have your newer code free of defensive nil checks.

Credits

What I call a nilable object, is well documented in the wild as the Option type. There are many implementations of it in Ruby land, with the most popular of them being Tom Stuart's monads. If you need more utils to deal with your nils, check it out.

Where nilable shines for me, is the simple implementation. That's all I need for my legacy projects.