From: Ryan Davis <ryand-ruby@...>
Date: 2012-10-26T05:54:44+09:00
Subject: Re: Name/symbol/object type clash? What is happening here?


On Oct 25, 2012, at 13:22 , Igor Pirnovar <lists@ruby-forum.com> wrote:

> Yossef Mendelssohn wrote in post #1081211:
> 
>> Just because something doesn't work the way you insist it must doesn't
>> mean it's broken.

exactly.

> If you claim that using accessors and '@' variables when reopening
> Struct classes with class idiom isn't broken, that's fine, but my last
> example I gave, clearly indicates differently!

Clearly? No. Your example is wrong, as shown by a simple -w:

9999 % ruby19 -w
 S = Struct.new(:num)
 class S
   attr_accessor :num
   def initialize(n); @num=n+5; end
   def num=(n); @num = n+5; end
 end
-:3: warning: method redefined; discarding old num
-:3: warning: method redefined; discarding old num=
-:5: warning: method redefined; discarding old num=

Reimplementing the accessors breaks the explicit contract of Struct. There's no point in doing so at all and your example is simply wrong. Breaking the contract of initialize is also wrong, you're not even calling super.

> If you do not need it to
> be consistent in those simple circumstances you use Struct idiom, that

Struct is not an idiom. It is a class. Its internals are an implementation detail. From the very first line of the rdoc on the class: "A Struct is a convenient way to bundle a number of attributes together, USING ACCESSOR METHODS" (emphasis mine).

> by no means discredits a more elaborate use, which clearly is broken,
> redundant and inconsistent, as I have shown in my previous sample code
> snippet, where you need to annul the Struct by the {{ attr_accessor :num
> }} line when you reopen the 'S' class, in order to be able to define
> more elaborate custom initialization accessor methods.

"Be able to"? You're blowing this WAY out of proportion:

% ruby19 -w
S = Struct.new(:num)
class S
  def initialize n
    super
    self.num = n + 5
  end
end
p S.new(10).num # => 15

Looks like it is more than able to.

> Let's not waste any more time on this issue. I think we all can tolerate
> this apparent glitch. At the same time reiterating that there should be
> as few exceptions as possible in the language grammar and its use
> certainly is not an out of line proposition.

This has nothing to do with grammar. Again, Struct is a class, not grammar.