Assignment function in RoR (Rails)

Question

I have been following this tutorial, online

http://ruby.railstutorial.org/chapters/sign-in-sign-out?version=3.2#top

and in part 8.2.3 there is something strange that I dont get. It says about this method:

module SessionsHelper

  def sign_in(user)
    cookies.permanent[:remember_token] = user.remember_token
    current_user = user
  end
end

and mentions that

current_user = user

is an assignment that has to be defined.This is strange cause in most languages i used so far when I want to assign a value I just use the "=" sign.

so he goes on defining this function:

 def current_user=(user)
    @current_user = user
  end

why didn't he just use before?

module SessionsHelper

  def sign_in(user)
    cookies.permanent[:remember_token] = user.remember_token
    @current_user = user
  end
end

is the above approach wrong?

Answer 1

@current_user is an instance variable. It is considered a good practice not to expose your naked instance variables to the whole world. Instead, you define getter and setter for it. In setter, for example, you can do validity checks. Or trigger callbacks. Or push/pop some state.

It's just plain more convenient, safe and flexible. At the cost of few lines of code.

Also, in ruby this is enforced at language level. You can't simply access instance variables.

class Foo
  def initialize
    @bar = 1
  end
end

puts Foo.new.@bar # raises exception