Re: Why use references?

You also might want to modify an arg to a subrutine. E.G.

With References

sub increment {
    my $arg_ref = shift;
    $$arg_ref++;
    if (is_bad($$arg_ref)) {
        return "FAILURE!";
    } 
    return undef;
}

my $num = 0;
my $err;

$err = increment(\$num);
if ($err) {
    die $err;
}

print "$num\n";
[download]

Without References

sub increment {
    my $arg = shift
    if (is_bad($arg)) {
        die "FAILURE";
    }
    return ++$arg;
}
my $num = 0;

$num = increment($num);

print "$num\n";
[download]

I don't think my sub that uses references is any better than the one that doesn't. It just shows two ways of doing the same thing.

Because you pass $num as a reference, the subrutine can change num. Then you can use the function's return for something else.

Update: chas! I've fixed the example to use ++$arg rather than $arg++.

AND! Woah. Baked my noodle with that one. So the only reason I've been convinced that subrutine args were passed as values was because I was using shift all the time!? Man... aye aye aye...

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Re^2: Why use references? by chas (Priest) on Dec 12, 2005 at 01:55 UTC
In your "Without References" example, don't you need `return ++$arg;`? (and a semicolon after `shift`?) Also, consider the following: `sub increment { ++$_[0]; } $num=0; increment($num); print $num,"\n";` [download] which shows that args are passed "by reference" by default. Of course, it may not be good style to alter @_ in this way, but the point is that you don't need to pass a reference to alter the argument inside the sub. (Updated to make less confusing.)	[reply] [d/l] [select]

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Re^2: Why use references?
by chas (Priest) on Dec 12, 2005 at 01:55 UTC

return ++$arg;

shift

sub increment {
     ++$_[0];
}
$num=0;
increment($num);
print $num,"\n";
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