Forum: Ruby Nuby - why does my #inspect misbehave?

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A0c079a7c3c9b2cf0bffebd84dc578b0?d=identicon&s=25 unknown (Guest)
on 2006-03-03 02:33
(Received via mailing list)
I'm working through a few exercises to teach myself Ruby. One of them
is the creation of a deck of cards along with all the usual
operations one performs upon them.

I override the Object#inspect method to pretty-print my card values,
but it doesn't always get called. Whether or not it gets called
depends on the **absence** of a line in #print_playing_deck. Here is
my code stripped down to the basics.

class Card < Object
   attr_reader :suit, :value

   protected
   attr_writer :suit, :value

   public
   def initialize(suit = "Joker", value = 15)
     @suit = suit
     @value = value
   end

   def inspect
       puts "#{self.value} of #{self.suit}s"
   end
end

class CardDeck < Card
   attr_reader :size

   SUITSIZE = 13

   def initialize(size = 52)
     @size = size

     @playing_deck = Array.new(@size) do |index|
       case index
       when *(0..12)
         Card.new("Heart", index + 1)
       end
     end
     @number_remaining = @playing_deck.length
   end

   def print_playing_deck
     @playing_deck.each do |card|
       puts card
     end
     # WEIRD!! If I have any code after this loop, my Card#inspect is
not called.
     # In this case I have a "puts" but it could even be arithmetic
expressions preventing
     # the #inspect from working
     #puts "#{@playing_deck.length} cards in deck"
   end

end


And here is the output:


irb(main):001:0> load 'ex.rb'
=> true
irb(main):002:0> d=CardDeck.new(5)
of s
=>
irb(main):003:0> d.print_playing_deck
#<Card:0x65b4>
#<Card:0x63e8>
#<Card:0x62a8>
#<Card:0x61cc>
#<Card:0x6168>
5 cards in deck
=> nil
######## comment out the "puts" in #print_playing_deck and reload
irb(main):004:0> load 'ex.rb'
./ex.rb:22: warning: already initialized constant SUITSIZE
=> true
irb(main):005:0> d.print_playing_deck
#<Card:0x65b4>
#<Card:0x63e8>
#<Card:0x62a8>
#<Card:0x61cc>
#<Card:0x6168>
1 of Hearts
2 of Hearts
3 of Hearts
4 of Hearts
5 of Hearts
=> [, , , , ]

I don't understand why my Card#inspect method doesn't print anything
to stdout when there is code after the loop. Is this just a weird
artifact of irb?

BTW, running on OSX with darwinports Ruby 1.8.4.
E34b5cae57e0dd170114dba444e37852?d=identicon&s=25 Logan Capaldo (Guest)
on 2006-03-03 02:45
(Received via mailing list)
On Mar 2, 2006, at 8:30 PM, cremes.devlist@mac.com wrote:

>   attr_reader :suit, :value
>   def inspect
>     @size = size
>   def print_playing_deck
>
> =>
> ./ex.rb:22: warning: already initialized constant SUITSIZE
> 4 of Hearts
> 5 of Hearts
> => [, , , , ]
>
> I don't understand why my Card#inspect method doesn't print
> anything to stdout when there is code after the loop. Is this just
> a weird artifact of irb?
>
> BTW, running on OSX with darwinports Ruby 1.8.4.
>

As a general rule #inspect is not supposed to print anything it is
supposed to return a string. Likewise in this case I believe your
inspect method is better named "to_s" since it gets you a string
representation of the object, not a peek into the objects internal
state. I don't know what the cause of your bug is though. Irb will
usually print the inspect string of an evaluated expression on its
own though, and puts returns nil. So when irb does the equivalent of
p a_card its going to get back nil which is gonna be converted to the
empty string. This may be part of your problem, but first I would
suggest changing your code to match the usual ruby conventions and
secondly try running the code outside of irb.
1fba4539b6cafe2e60a2916fa184fc2f?d=identicon&s=25 unknown (Guest)
on 2006-03-03 03:10
(Received via mailing list)
Hi --

On Fri, 3 Mar 2006, cremes.devlist@mac.com wrote:

> I'm working through a few exercises to teach myself Ruby. One of them is the
> creation of a deck of cards along with all the usual operations one performs
> upon them.
>
> I override the Object#inspect method to pretty-print my card values, but it
> doesn't always get called. Whether or not it gets called depends on the
> **absence** of a line in #print_playing_deck. Here is my code stripped down
> to the basics.
>
> class Card < Object

Don't inherit from Object -- it happens automatically :-)

> def inspect
>     puts "#{self.value} of #{self.suit}s"
> end

This is having a weird effect on what you get in irb, like when you
create a deck, you get:

   of s

because it's trying to print that string.  #inspect should really just
return a string, not print it out (as I think Logan also mentioned).

> def print_playing_deck
>   @playing_deck.each do |card|
>     puts card
>   end

One of the great rites of passage for new Rubyists is learning that:

   puts array

does the iterating for you :-)  So that should be just:

   puts @playing_deck

>
> #<Card:0x61cc>
> #<Card:0x6168>
> 5 cards in deck
> => nil

That nil is the return value of puts, which is the last expression in
#print_playing_deck.

> 1 of Hearts
> 2 of Hearts
> 3 of Hearts
> 4 of Hearts
> 5 of Hearts
> => [, , , , ]

Now the last expression in #print_playing is @playing_deck (the return
value of the call to #each).  To display @playing_deck, irb calls
#inspect on each element.  The side-effect of this is that "1 of
Hearts" etc. gets printed.  The return value of #inspect, however, is
nil (the value of puts), which is why you get the weird little array
of nothings at the end.


David

--
David A. Black (dblack@wobblini.net)
Ruby Power and Light (http://www.rubypowerandlight.com)

"Ruby for Rails" chapters now available
from Manning Early Access Program! http://www.manning.com/books/black
Bc6d88907ce09158581fbb9b469a35a3?d=identicon&s=25 James Britt (Guest)
on 2006-03-03 03:25
(Received via mailing list)
dblack@wobblini.net wrote:

>
> One of the great rites of passage for new Rubyists is learning that:
>
>   puts array
>
> does the iterating for you :-)



:(



--
James Britt

"Programs must be written for people to read, and only incidentally
  for machines to execute."
   - H. Abelson and G. Sussman
   (in "The Structure and Interpretation of Computer Programs)
1fba4539b6cafe2e60a2916fa184fc2f?d=identicon&s=25 unknown (Guest)
on 2006-03-03 03:43
(Received via mailing list)
Hi --

On Fri, 3 Mar 2006, James Britt wrote:

>
> :(

?


David

--
David A. Black (dblack@wobblini.net)
Ruby Power and Light (http://www.rubypowerandlight.com)

"Ruby for Rails" chapters now available
from Manning Early Access Program! http://www.manning.com/books/black
4c8a9bec5a27b66b28d3c5cddeb70e93?d=identicon&s=25 Mr. Big (Guest)
on 2006-03-03 03:46
unknown wrote:
> Hi --
>
> On Fri, 3 Mar 2006, James Britt wrote:
>
>>
>> :(
>
> ?

O-('_' Q)
Bc6d88907ce09158581fbb9b469a35a3?d=identicon&s=25 James Britt (Guest)
on 2006-03-03 05:16
(Received via mailing list)
dblack@wobblini.net wrote:
>>>
>>> does the iterating for you :-)
>>
>>
>>
>>
>> :(
>
>
> ?


POGSFJ

(I'll refrain from invoking P*LS)



James
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