From: John Winters <john@...>
Date: 2008-08-01T06:17:40+09:00
Subject: Re: Needing help with which to_s gets called

Thanks to all for some very useful pointers.

On Thu, Jul 31, 2008 at 4:41 PM, Sebastian Hungerecker
<sepp2k@googlemail.com> wrote:
[snip]
> You're right. join special cases arrays as well, joining nested arrays as well
> instead of to_sing them (that or it just calls flatten on the array before
> starting it's work).

That certainly seems to be the case, as witnessed by the following
snippet.

a = ["a", "b", "c"]
b = ["d", "e", "f"]
c = Array.new
c << a
c << b
puts "Size of c is #{c.size}"
puts c.join(", ")

which produces:

Size of c is 2
a, b, c, d, e, f

It looks very much like join will flatten anything which it thinks it 
can.

Gregory Brown wrote:
> 
> I guess this is an example of core class special cases that I was
> worried about in an earlier thread today.
> 
> I really don't think it's a good practice to subclass core classes
> unless you are only adding new behaviour.
> Wrapping and delegating is much more predictable.

Thank you - I'll take note of that.  My original problem was that I have 
a structure involving nested arrays and I wanted them to print out with 
the nesting apparent.  Sub-classing Array seemed the obvious way to do 
it, but perhaps not.

> That having been said, the problem goes away if you first explicitly
> map using to_s before the join(), but this is an indication of the
> kind of hacks subclassing core objects like Array will force upon you
> :-/
> 
> 
>  def to_s
>    "[Baker: #{@contents.map { |e| e.to_s }.join(", ")}]"
>  end

Adding to the snippet above:

puts c.map { |e| e.to_s }.join(", ")

Produces:

abc, def

So I now have a choice of two ways to do it.

Cheers,
John
-- 
Posted via http://www.ruby-forum.com/.