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Ruby Programming Language

Overriding to_s


Hi,

I'm playing around with ruby trying to understand whats going on, and
here is something I don't understand.

class ZNum
  def initialize(n)
    @n=n
  end
  def to_s
    self.class
  end
end

n = ZNum.new(1234)

puts n            # prints #<ZNum:0xb75dfcc8>
puts n.to_s     # prints ZNum

In both cases it uses ZNum#to_s, but the results are different. Why?

/kim

On 29.05.2007 10:51, kimer@gmail.com wrote:

Because puts will revert to something else (likely #inspect) if the
result of to_s is not String.

irb(main):001:0> class Foo
irb(main):002:1> def to_s; self.class.to_s end
irb(main):003:1> end
=> nil
irb(main):004:0> puts Foo.new
Foo
=> nil

Kind regards

        robert

Not able to understand what you are actually asking. Can you put little
detail on this.

--
Posted via http://www.ruby-forum.com/.

On May 29, 11:04 am, Robert Klemme <shortcut@googlemail.com> wrote:

My understanding of puts is that it puts the result of to_s.
puts n and puts n.to_s are the same then and should in my example
print the same.
But they don't and that is for me a bit annoying because I thought I
understood what was going on.

/kim

On 29.05.2007 14:50, kimer@gmail.com wrote:

No, they are not the same because to_s returns the class.  You really
have "puts foo" and "puts Foo" ("puts ZNum" in your case).

> But they don't and that is for me a bit annoying because I thought I
> understood what was going on.

Please carefully reread my comment.  Since you chose to make to_s return
something that is *not a String* you get the behavior that you see.

        robert

Yes, but what do you expect "puts" to do when it calls to_s on an object,
but the result is not a string? Raise an exception perhaps? It's more
friendly for puts to have a fallback behaviour.

Note: there's one other special case I'm aware of. If you do
   puts nil
then you get the string "nil" printed (plus newline). However, nil.to_s is
the empty string.

Regards,

Brian.

On May 29, 12:15 pm, Rohan Dey <rohan@gmail.com> wrote:

I'm working on an interface for some legacy data.
The legacy data will be stored in objects as ruby numbers (fixnum,
bignum and float), but I need to override ruby's number formating. My
example above has no practical value, it's just some odd behavior that
I would like to understand before I design my legacy interface.

/kim

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