Question

I recently discovered that in Python, you can do this:

array = [1, 2, 3, 4]
if 3 in array:
  print("Yep!")

Then, I thought to myself: “Mh, why is it different in Ruby? if 3 in array is more readable than if array.include? 3.” Then, I realized, that Ruby is pure OOP and this approach is keyword-based.

But still, I am wondering. If the Python approach is not OOP, why can’t there be another, shorter way in Ruby that is even more readable? When thinking, I don’t think “Does this list include that element?”, but “Is this element in that list?”.

Let’s assume, the following code was possible:

array = [1, 2, 3, 4]

if 3.in? array
  print "Yep!
end

I see that it is a turn-around from list.method(element) to element.method(list).
So, I am wondering: Which ruby principles/rules speak against the above-metioned code?

EDIT: Oops, I wrote “keyboard-based” but meant of course “keyword-based”. To emphasize this: I am not looking for methods that behave like the in? method; I am looking for reasons why it is not implemented in Ruby that way.

Answer 1

Which ruby principles/rules speak against the above-metioned code?

It’s not a Ruby principle, but rather the general OOP principle of encapsulation: the Fixnum class should not need to know anything about arrays. However, because Array’s primary responsibility is to contain collections of objects, #in? or #include? clearly falls under Array’s responsibility.