Ruby - Private vs Protected - What's the difference?
What’s the difference?
Private Methods Explained
@freddie = Person.new
@freddie.hows_it_going?
# => "oh dear, i'm in great pain!"
class Person
# public method
def hows_it_going?
how_are_your_underpants_feeling?
end
private
def how_are_your_underpants_feeling? # private method
puts "oh dear, i'm in great pain!"
end
end
We can ask Freddie how things are going given it’s a public method. That’s perfectly valid. And it’s normal and accepted.
But…the only person who can know how Freddie’s underpants situation is, is Freddie himself. It would not do for random strangers to reach into Freddy’s underpants and test out the situation – no, no – it’s very, very private, and we don’t want to expose what’s private to the outside world.
@freddie.how_are_your_underpants_feeling?
# => # NoMethodError: private method `how_are_your_underpants_feeling?' called
Protected Methods Explained
Ok now what’s the deal with protected? Now consider this situation:
class Person
protected
def gimme_your_credit_card! # protected method
puts "Fine. Whatever. Here it is: 1234-4567-8910"
end
end
class Rib < Person
end
class Wife < Rib # wife inherits from Rib
def i_am_buying_another_handbag_with_your_card(husband)
husband.gimme_your_credit_card!
end
end
@husband = Person.new
@mrs = Wife.new
@mrs.i_am_buying_another_handbag_with_your_card(@husband)
# => puts "Fine. Whatever. Here it is: 1234-4567-8910"
We’re somewhat ok with mrs getting our credit card details, given mrs is flesh of our flesh, inherited from Person, but we don’t want random individuals getting access to our credit card details.
If we tried to do that outside the subclass, it would fail:
@mrs = Wife.new
@mrs.gimme_your_credit_card!
# => protected method gimme_your_credit_card! called for #<Wife:0x00005567b5865818> (NoMethodError)