From: Igor Pirnovar <lists@...>
Date: 2012-10-27T16:14:04+09:00
Subject: Re: Name/symbol/object type clash? What is happening here?

Robert, you continue pretending that you proved my point of view wrong
by always providing only half of the solution, because you simply can
not satisfy both requirements simultaneously.  Namely, I require that
both 'initialize' method as well as the attribute accessor (i.e.: the
setter) method work correctly in tandem when an expression rather than
the simple assignment is required.

This code of yours simply doesn't work when using Struct, (nor does it
work when you try to reopen 'S' as class, as was initially argued at the
beginning of this thread):

  S = Struct.new :a do
    def initialize(a); self.a = a + 5; end
    alias _a= a=
    def a=(n) self._a= n + 5; end
  end

  s = S.new(0)
  p s.a    #=> 10 WRONG!!!
  s.a = 100
  p s.a    #=> 105

With the exception of 'to_s' method, you see here the equivalent of the
above code snippet of yours, this time using only classes (which BTW
works correctly):

  class A
    attr_accessor :num
    def initialize(n); @num=n; end
    def to_s; "#{self.class}: num=#@num"; end
  end

  class B < A
    def initialize(n); super; @num = n + 5; end
    def num=(n) @num = n + 5; end
  end

  a = A.new(0)
  p "After: a=A.new(0) ... #{a}"  #=> ... A: num=0
  a.num = 100
  p "After: a.num=100 .... #{a}"  #=> ... A: num=100

  b = B.new(0)
  p "After: b=B.new(0) ... #{b}"  #=> ... B: num=5
  b.num = 100
  p "After: b.num=100 .... #{b}"  #=> ... B: num=105

Once again, Struct does not provide satisfactory solution to both above
stated initialization requirements, because it does not obey Ruby's '@'
instance variable semantics, and due to this now revealed Ruby grammar
inconsistency introduced by Struct, exposes broken blundering like yours
as you try to botch your way out of it, when Ruby compounds double
execution of expressions used in class/Struct initialization process
(see my comment in your code: #=> 10 WRONG!!!).

Regards, igor

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