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)
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 everycat
object inside it. Since it holds the things that are in common across allcat
s, eachcat
can just think about the things it knows and does special.Say we have a cat object called
tom
. If we wanttom
to do something, we have to sendtom
a message. We can sendtom
a message in Ruby by using a.
and the name of the thing we wanttom
to do. When we writetom.chase
in Ruby, we are writing a message in three parts.tom
gets the message,.
means we're sending a message, andchase
is the method we're sending.tom.chase
means, "tom
, pleasechase
"tom
is an object, a box of info and actions. Whentom
gets thechase
message, he'll look inside his box for how tochase
. If he can't find any instructions labeledchase
, he will look outside his box in the bigCat
box to see if there are any instructions labeledchase
there.Since everything in Ruby is an object, you better believe that
Cat
is not the biggest box.Cat
might be inside another box calledAnimal
. Iftom
doesn't find any instructions for how tochase
inCat
, he'll check the giantAnimal
box. He will keep looking in bigger and bigger boxes until he either finds some instructions labelledchase
or he gets to the box the size of the Ruby universe—theBasicObject
box.If
tom
can't find any instructions in theBasicObject
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.
This is crystal clear @levi ! Thank you so much for this. Love the Russian dolls-y metaphor here. 👏
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.
manning.com/books/the-well-grounde...
P.S. No affiliation, just a happy reader (and I got to review the 1st edition)
Haven't found an answer yet, but the beginners' intro to objects and classes is now live on dev.to @ben 👉 dev.to/mercier_remi/a-beginners-in...