On Sat, Oct 27, 2012 at 9:14 AM, Igor Pirnovar <lists / ruby-forum.com> wrote:
> 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.

I have understood that but apparently you did not read my posting
properly or tested the code I provided.

> 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

Igor, that was not my code.  Your claim is wrong.  I posted this upthread:

S = Struct.new :num do
  alias _initialize initialize
  def initialize(n)
    super
    self.num = n
  end

  alias _num= num=
  def num=(n) self._num= n + 5 end
end

If you try that out you'll see this:

irb(main):011:0> S.new(0).num
=> 5
irb(main):012:0> x = S.new 0
=> #<struct S num=5>
irb(main):013:0> x.num
=> 5
irb(main):014:0> x.num = 10
=> 10
irb(main):015:0> x.num
=> 15

However, there's still a hole

irb(main):016:0> x[:num] = 5
=> 5
irb(main):017:0> x.num
=> 5

This (along with the fact that Ruby will return the reference passed
to an assignment and ignore the return value of the method)
demonstrates that the whole approach of changing the value while
assigning is at least questionable.

> Once again, Struct does not provide satisfactory solution to both above
> stated initialization requirements,

See upthread.

> because it does not obey Ruby's '@'
> instance variable semantics, and due to this now revealed Ruby grammar

See above, this has nothing to do with grammar and also it is
completely legal for Ruby classes to not exhibit their state via
instance variables.

"Grammar" in context of programming languages has a very specific meaning:
http://en.wikipedia.org/wiki/Formal_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!!!).

Please stick to the facts.

These statements of yours brought me into the discussion:

On Tue, Oct 23, 2012 at 7:44 PM, Igor Pirnovar <lists / ruby-forum.com> wrote:
> Due to the problems shown above, perhaps Struct should be taken out of
> Ruby paradigm all together.
>
> [...] The use of 'Struct' should also be
> discouraged, and even worse, mixing Struct with class definitions and
> usage is ill advised.

That's like asking to ban hammers from all hardware stores because
they are badly suited to tighten screws.  You are claiming that Struct
is ill suited for a particular use case (which is debatable in itself)
and infer that Struct is generally not useful (or even harmful) and
should be taken out of the language.  You are free to use or not use
Struct based on your judgement, but please refrain from claiming that
Struct is useless, harmless or should be removed from the library on
such weak evidence.

Cheers

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/