Why are setter methods not used in initialization?

Recently I've been reading "Practical Object Oriented Design in Ruby", and I noticed one of the best practices was to use accessor methods instead of directly grabbing the @instance_variable . For example:

class Foo
  attr_accessor :bar

  def initialize(my_argument)
    @bar = my_argument
  end

  # bad
  # def lorem_ipsum
  #     @bar * 999
  # end

  # good
  def lorem_ipsum
    bar * 999
  end

end

It makes sense to keep things DRY, and, in case I need to process @bar somehow before actually grabbing its value. However, I noticed that the initialize method sets the value of the @bar instance variable directly:

class Foo
  attr_accessor :bar

  def initialize(my_argument)
    @bar = my_argument #<-- why isn't self.bar = my_argument used here?
  end

Is there a reason for this? Shouldn't the setter method be used instead of directly using the = operator to set the value of the instance variable?

---

You're right, it would make much more sense to do

class Foo
  attr_accessor :bar

  def initialize(my_argument)
    self.bar = my_argument
  end
end

Arguments differ as to whether you should respect encapsulation within the object itself or not, but if you believe in that, then, yes, you should do this.

---

The initializer SETS the value upon initialization. The accessor lets you access (read/write) via the symbol after the object is already instantiated.

This post might help you understand: What is attr_accessor in Ruby?

---

Actually, the setter can be used in initialize the same as in other methods, but setter cannot be used without a receiver.

I think you can use a_foo.bar= or self.bar= , but cannot use bar= without a receiver, because, in the later case, bar will be treated as a local variable rather than a setter method:

class Song
  attr_accessor :name
  def initialize(name)
    self.name = name
  end
  def test_setter1(value)
    @name = value
  end
  def test_setter2(value)
    name = value #name is local variable
  end
end

s = Song.new("Mike")
p s
s.test_setter1("John")
p s
s.test_setter2("Rosy")
p s

This results in:

#<Song:0x23a50b8 @name="Mike">
#<Song:0x23a50b8 @name="John">
#<Song:0x23a50b8 @name="John">

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