From: "Matthias Wächter" <matthias@...>
Date: 2011-12-09T02:04:07+09:00
Subject: Re: Confusing results from string multiplication

On 08.12.2011 17:16, Rob Marshall wrote:
> I thought, maybe this is a problem with irb, so I wrote a little
> program:
>
> #!/usr/bin/env ruby
>
> puts (11.to_s * 2)
> puts (11.to_s *2)
> puts (11.to_s*2)
>
> And when I run it, I see:
>
> 1111
> 1011
> 1111

but it works correctly for other numbers. try

puts (10.to_s *2)

;)

Well, it appears that "*2" becomes an argument to to_s, so your second 
line of code is interpreted as

puts (11.to_s(*2))

and this strange looking argument to to_s is actually interpreted as a 
splat operator and becomes converted to the Fixnum 2, so what you’re 
actually requesting is a string containing the binary representation. 11 
as decimal is 0xb in hex or, as you see it, 1011 in binary.

There is quite some magic to splat operator’s behavior in some cases. 
For example, the splat cannot stand on its own like a normal expression. 
So the following is invalid:

*[1,2]
*x
*2

but this is valid:

x=*[1,2]
y=*x
z=*2

Another magic – from my POV – is happening when assigning arrays to 
multiple variables. Splat doesn’t seem to play a big role here, and 
sometimes it is hard to judge how such an assignment will end, 
considering differing data types on the RHS.

                       # actual              # expected
a=[1,2,3]             # a=[1,2,3]
b=*[1,2,3]            # b=[1,2,3]           # b=1
c,d=[1,2,3]           # c=1, d=2            # c=[1,2,3], d=nil
e,f=*[1,2,3]          # e=1, f=2
g,h=a                 # g=1, h=2            # g=[1,2,3], h=nil
a=2
i,j=a                 # i=1, j=2

> Can anyone explain why the '11.to_s *2' gave me 1011? Is this a 1.8.7
> problem? The Ruby version on my Mac OS X Lion system is: ruby 1.8.7
> (2010-01-10 patchlevel 249) [universal-darwin11.0].

Same here with 1.9.3-p0 Linux 64bit.

– Matthias