# Nuby - why does my #inspect misbehave?

**URL:** <https://www.ruby-forum.com/t/nuby-why-does-my-inspect-misbehave/76084>\
**Category:** Ruby\
**Created:** [March 3, 2006, 2:33am UTC](https://www.ruby-forum.com/t/nuby-why-does-my-inspect-misbehave/76084 "2006-03-03T02:33:50Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [March 3, 2006, 2:33am UTC](https://www.ruby-forum.com/t/nuby-why-does-my-inspect-misbehave/76084/1 "2006-03-03T02:33:50Z")

</div>

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.

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<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [March 3, 2006, 2:45am UTC](https://www.ruby-forum.com/t/nuby-why-does-my-inspect-misbehave/76084/2 "2006-03-03T02:45:55Z")

</div>

On Mar 2, 2006, at 8:30 PM, removed\_email\_address@domain.invalid 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.

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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [March 3, 2006, 3:10am UTC](https://www.ruby-forum.com/t/nuby-why-does-my-inspect-misbehave/76084/3 "2006-03-03T03:10:01Z")

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Hi –

On Fri, 3 Mar 2006, removed\_email\_address@domain.invalid 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 (removed\_email\_address@domain.invalid)  
Ruby Power and Light ([http://www.rubypowerandlight.com](http://www.rubypowerandlight.com))

“Ruby for Rails” chapters now available  
from Manning Early Access Program! [Ruby for Rails](http://www.manning.com/books/black)

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [March 3, 2006, 3:43am UTC](https://www.ruby-forum.com/t/nuby-why-does-my-inspect-misbehave/76084/4 "2006-03-03T03:43:11Z")

</div>

Hi –

On Fri, 3 Mar 2006, James B. wrote:

> ☹

?

David

–  
David A. Black (removed\_email\_address@domain.invalid)  
Ruby Power and Light ([http://www.rubypowerandlight.com](http://www.rubypowerandlight.com))

“Ruby for Rails” chapters now available  
from Manning Early Access Program! [Ruby for Rails](http://www.manning.com/books/black)

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [March 3, 2006, 3:25am UTC](https://www.ruby-forum.com/t/nuby-why-does-my-inspect-misbehave/76084/5 "2006-03-03T03:25:06Z")

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removed\_email\_address@domain.invalid wrote:

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

☹

–  
James B.

“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)

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [March 3, 2006, 3:46am UTC](https://www.ruby-forum.com/t/nuby-why-does-my-inspect-misbehave/76084/6 "2006-03-03T03:46:03Z")

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unknown wrote:

> Hi –
> 
> On Fri, 3 Mar 2006, James B. wrote:
> 
> > ☹
> 
> ?

O-(’\_’ Q)

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [March 3, 2006, 5:16am UTC](https://www.ruby-forum.com/t/nuby-why-does-my-inspect-misbehave/76084/7 "2006-03-03T05:16:33Z")

</div>

removed\_email\_address@domain.invalid wrote:

> > > does the iterating for you 🙂
> > 
> > ☹
> 
> ?

POGSFJ

(I’ll refrain from invoking P\*LS)

James