From: Stefano Crocco <stefano.crocco@...>
Date: 2007-01-05T18:47:09+09:00
Subject: Re: puts returns nil?

Alle 10:30, venerd狸 5 gennaio 2007, Arfon Smith ha scritto:
> Hi, I'm sorry to be asking such a daft question but I need a concept
> explaining....
>
>
> I'm working through the excellent Chris Pine book 'Learn to program' and
> I don't get one of the examples he gives.  In particular I don't follow
> the following example:
>
>
> def say_moo number_of_moos
>   puts 'mooooooo...' * number_of_moos
>   'yellow submarine'
> end
>
> x = say_moo 3
> puts x.capitalize + ', dude...'
> puts x + '.'
>
> Now the output from this is:
>
> mooooooo...mooooooo...mooooooo
> Yellow submarine, dude...
> yellow submarine
>
> -------------
>
> OK, so here's the problem, I _don't_ get why it doesn't return the
> following:
>
>
> mooooooo...mooooooo...mooooooo
> Yellow submarine, dude...
> mooooooo...mooooooo...mooooooo
> yellow submarine
>
> -------------
>
> Why do we get one set of 'moos' but not a second?
>
> Sorry for such a newbiee question.
>
> Cheers
>
> arfon

say_moo does two separate things:
1- writes the string 'mooooooo...' on the screen number_of_moos times
2- returns the string 'yellow submarine'
The call to puts in the definition of say_moo has nothing to do with say_moo's 
return value, which is determinated by the method's last line: 'yellow 
submarine'. 

Writing x=say_moo 3 will put in x only the string 'yellow submarine', because 
this is what say_moo returns. In other words, the line 
mooooooo...mooooooo...mooooooo is written by a side effect of say_moo; the 
other two lines are produced by your own puts statements.

To get the output you expected (well, not exactly, captialize would work a 
little differently), say_moo should have defined like this:

def say_moo number_of_moos
  mooooooo...' * number_of_moos+"\nyellow submarine"
end

In this case, say_moo wouldn't write nothing on the screen by itself,  but 
would return the string
"mooooooo...mooooooo...mooooooo
yellow submarine"
which would be written twice by your puts statements

I hope this helps

Stefano