DEV Community

Rémi Mercier
Rémi Mercier

Posted on • Updated on

How does Ruby method lookup work? 🤔

Salut people!

I'm in the process of writing a beginners' introduction to Ruby classes and objects (18th Nov update: it's live!).

While talking with a friend about how classes inherit from their ancestors and the parent Class class, we realized we didn't know how exactly the method lookup works in Ruby.

My first (and wild) guess was: Ruby uses the method(:some_method).owner then check the ancestors' chain. But can't really wrap my head around this.

Anyone around here would like to have a go? 🙏

Top comments (4)

levi profile image
Levi • Edited

Everything in the world of Ruby is an object. An object is a box of information (data) and actions (methods). If we treated a cat like an object, it would have data like a height or attitude or age. It would also have behaviors like purring, scratching, and sleeping. Because all cats share similar actions and kinds of information, we can put them in an even bigger box called Cat.

Cat with a capital "C" is a class, and it's an object with the types of information and actions that can be found in every cat object inside it. Since it holds the things that are in common across all cats, each cat can just think about the things it knows and does special.

Say we have a cat object called tom. If we want tom to do something, we have to send tom a message. We can send tom a message in Ruby by using a . and the name of the thing we want tom to do. When we write in Ruby, we are writing a message in three parts. tom gets the message, . means we're sending a message, and chase is the method we're sending. means, "tom, please chase"

tom is an object, a box of info and actions. When tom gets the chase message, he'll look inside his box for how to chase. If he can't find any instructions labeled chase, he will look outside his box in the big Cat box to see if there are any instructions labeled chase there.

Since everything in Ruby is an object, you better believe that Cat is not the biggest box. Cat might be inside another box called Animal. If tom doesn't find any instructions for how to chase in Cat, he'll check the giant Animal box. He will keep looking in bigger and bigger boxes until he either finds some instructions labelled chase or he gets to the box the size of the Ruby universe—the BasicObject box.

If tom can't find any instructions in the BasicObject box, a cry echoes through the Ruby universe, an error is raised, time stops, and the Ruby universe collapses until it's created again.

There's also a great StackOverflow thread on the Ruby method lookup path here.

mercier_remi profile image
Rémi Mercier

This is crystal clear @levi ! Thank you so much for this. Love the Russian dolls-y metaphor here. 👏

phallstrom profile image
Philip Hallstrom

The book "The Well-Grounded Rubyist" has IMHO the best coverage of this I've ever seen. Chapter 4 (and 5) are excellent and well worth the price of the book.

P.S. No affiliation, just a happy reader (and I got to review the 1st edition)

mercier_remi profile image
Rémi Mercier

Haven't found an answer yet, but the beginners' intro to objects and classes is now live on @ben 👉