From: Jeremy Bopp <jeremy@...>
Date: 2010-10-07T07:52:45+09:00
Subject: Re: Missing @ for instace variable in class, but no error message

On 10/6/2010 5:42 PM, Andrew Wagner wrote:
> attr_accessor actually defines a public instance method, named 'a'. That
> method can be called from both inside and outside the class. So, it's not an
> error, it's perfectly valid.

Beware of attempting to use the bare a= accessor within an instance
method though.  That will instead cause a variable named "a" to be
created with the the method's scope rather than use the a= accessor, so
@a won't be updated as expected.  If you want to use the a= accessor,
you need to use self.a = whatever.  e.g.:

class MyClass
  attr_accessor :a

  def change_a_bad(value)
    a = value
  end

  def change_a_good(value)
    self.a = value
  end
end

my_class = MyClass.new
my_class.a = 1

my_class.change_a_bad(2)
my_class.a                  # => 1  !!!

my_class.change_a_good(2)
my_class.a                  # => 2  :-)


-Jeremy