From: Stefano Crocco <stefano.crocco@...>
Date: 2008-06-15T04:12:33+09:00
Subject: Re: Definning "to_s" in a class -  inexpected result

On Saturday 14 June 2008, Andrés Suárez wrote:
> Hi,
>
> I'm trying to obtain the cards of a Deck in a string like
> "2s...KsAs2h...Ah2d...Ad2c...Ac". The problem with the folowing code is
> that in the end of the string appears "#<Deck:0x2bb5880>". Why? Can I
> avoid it?
>
> class Deck
>
>   SUITS = %w{s d h c}
>   RANKS = %w{2 3 4 5 6 7 8 9 T J Q K A}
>
>   def initialize
>    @cards = []
>    SUITS.each{ |s| RANKS.each{ |r| @cards << r+s } }
>   end
>
>   def popCard
>     @cards.pop
>   end
>
>   def to_s
>    @cards.map{ |card| print card}
>   end
>
> end
>
> d0 = Deck.new
> puts d0
>
>
> Regards,
> Andrés

There are two problems with your code. The first is the use of print in the 
to_s method. print displays its arguments on screen and returns nil. So, the 
return value of the @cards.map expression is an array filled with nil 
elements. The second problem lies in the fact that your to_s method returns an 
array.

You can solve both problems using the following definition of Deck#to_s:

def to_s
  @cards.join ' '
end

Since the elements of the @cards array are already strings, you don't need to 
convert them. Instead, you have to convert the array itself to a string: using 
join will convert each element of the array to a string, then concatenates 
them inserting a space between each pair.

I hope this helps

Stefano