From: Igor Pirnovar <lists@...>
Date: 2012-10-24T02:44:08+09:00
Subject: Re: Name/symbol/object type clash? What is happening here?

No doubt, the following code exhibits unacceptable inconsistencies:

  S = Struct.new(:num)
  class S; def change_to n; @num = n; end; end
  s = S.new(3)
  puts s.num     #=> s
  s.num = 4
  puts s.num     #=> 4
  s.change_to(5)
  puts s.num     #=> 4

Due to the problems shown above, perhaps Struct should be taken out of
Ruby paradigm all together.

However, except in limited initialization circumstances, the use of '@'
variables should be prohibited, and from the point of view of strict
OOP, it is, by convention! The use of 'Struct' should also be
discouraged, and even worse, mixing Struct with class definitions and
usage is ill advised.

The above problem can be solved if you use accessor methods in place of
'@' variable:

  S = Struct.new(:num)
  class S
    def show_num; puts "Show:#{self.num}"; end
    def change_num(n); self.num = n; end
  end

  s = S.new(100)
  puts s.num  #=> 100
  s.show_num  #=> Show:100

  def s.change_singleton_num(n); self.num = n; end   # <<< SOLUTION

  s.num = 1
  puts s.num  #=> 1
  s.show_num  #=> Show:1

  s.change_num(2)
  puts s.num  #=> 2
  s.show_num  #=> Show:2

  s.change_singleton_num(2000)
  puts s.num  #=> 2000
  s.show_num  #=> Show:2000

Regards, igor

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