From: Dave Bass <davebass@...>
Date: 2008-06-06T20:31:59+09:00
Subject: Re: A crosspost from the Perl Community

Eric Mahurin wrote:
> No, ruby is still call-by-value.  The "value" is an object reference
> (or simply an object in ruby terms).

So you pass a reference to a function. Isn't this call-by-reference???

Whatever the technicalities, what I mean is this. In Perl:

  sub upper
  {
    my $x = shift;
    $x =~ tr/a-z/A-Z/;
  }

  $a = "hello";
  upper($a);
  print $a;  # => "hello"

$a is unchanged because $x is a local copy of $a; changing $x leaves $a 
unchanged. But in Ruby:

  def upper(x)
    x.upcase!
  end

  a = "hello"
  upper(a)
  print a  # => "HELLO"

The original a is changed because upper has direct access to it. You can 
get the same effect in Perl using explicit referencing and 
dereferencing:

  sub upper
  {
    my $x = shift;
    $$x =~ tr/a-z/A-Z/;
  }

  $a = "hello";
  upper(\$a);
  print $a;  # => "HELLO"

Dave
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