Question

Can someone explain the difference between initializing “self” and having @variables when defining classes?

Here’s an example

class Child < Parent
  def initialize(self, stuff):
    self.stuff = stuff
    super()
  end
end

So in this case, wouldn’t I be able to replace self.stuff with @stuff? What’s the difference? Also, the super() just means whatever is in the Parent initialize method the Child should just inherit it right?

Answer 1

In general, no, self.stuff = stuff and @stuff = stuff are different. The former makes a method call to stuff= on the object, whereas the latter directly sets an instance variable. The former invokes a method which may be public (unless specifically declared private in the class), whereas the latter is always setting a private instance variable.

Usually, they look the same because it is common to define attr_accessor :stuff on classes. attr_accessor is roughly equivalent to the following:

def stuff
  @stuff
end

def stuff=(s)
  @stuff = s
end

So in that case, they are functionally identical. However, it is possible to define the public interface to allow for different results and side-effects, which would make those two “assignments” clearly different:

def stuff
  @stuff_called += 1    # Keeps track of how often this is called, a side effect
  return @stuff
end

def stuff=(s)
  if s.nil?             # Validation, or other side effect. This is not triggered when setting the instance variable directly
    raise "Argument should not be nil"
  end
  @stuff = s
end