From: Dave Thomas <Dave@...>
Date: 2002-04-05T07:09:27+09:00
Subject: Re: Kernet methods and IO methods

Yohanes Santoso <ysantoso@jenny-gnome.dyndns.org> writes:
> Markus Jais <info@mjais.de> writes:
> 
> > that is, the IO#gets  is completely different from Kernel's "gets" method.
> > I do not mean, that they work differently, but they are implemented
> > seperately in Kernel and again in IO.
> 
> Think of Kernel#gets as:
> def Kernel.gets 
>    STDIN.gets
> end

Actually, it's slightly more complicated than that.

If there are command line file names present, gets will read from each
in turn. This doesn't affect STDIN or $stdin.

Thus
      while line = gets
         puts line
      end

will read from files specified on the command line (if any) while
STDIN.gets will read from standard input regardless.

If there are no command line file names present, Ruby initially sets
$stdin to STDIN (the process's standard input), and then reads using
$stdin as a file. In these circumstances, you can set the value of
$stdin yourself. If that object is an IO object, it will be read
from. It it's another class, its #gets method will be called.

     class Dave
       def initialize
         @values = %w{d a v e}
       end

       def gets
         @values.shift
       end
     end

     $stdin = Dave.new

     while line = gets
       puts line
     end


However, I'm beginning to wonder if it's possibly a bug that the above
program acts differently depending on whether it's called with command
line arguments. 

Cheers


Dave