--- Michael Fowler <[EMAIL PROTECTED]> wrote:
> You could also make your own print function that appends to the variable of
> your choice:
>
> sub append_and_print (\$@) {
> my($var_ref, @stuff_to_print) = @_;
>
> $$var_ref = '' unless defined($$var_ref);
> my $sep = defined($,) ? $, : "";
> $$var_ref .= join($sep, @stuff_to_print);
>
> print @stuff_to_print;
> }
>
> append_and_print($stuff_to_print, "hi");
Michael,
I'd be very careful about recommending something like the above to someone who's not
terribly
familiar with Perl. It's going to bite them and bite them badly.
I don't particularly care for prototypes
(http://www.perl.com/pub/a/language/misc/fmproto.html),
so I rarely use them (some many have seen the "try/catch" snippet I posted the other
day (and
stole from someone else). That used prototypes, so just pretend I didn't mention it :)
One of the problems with prototypes is that they are not prototypes, at least not in
the sense
that other programming languages use them. Instead, they allow us, amongt other
things, to force
function arguments into a particular context. In your example, the first argument
*doesn't* have
to have a scalar value. If you pass an array or hash reference as the first argument,
it is
silently coerced into scalar context. Run the following snippet:
use strict;
use warnings;
sub append_and_print(\$@);
my $stuff_to_print = ["Foo"];
append_and_print $stuff_to_print, "hi", " there\n";
print $stuff_to_print;
sub append_and_print (\$@) {
my($var_ref, @stuff_to_print) = @_;
$$var_ref = '' unless defined($$var_ref);
my $sep = defined($,) ? $, : "";
$$var_ref .= join($sep, @stuff_to_print);
print @stuff_to_print;
}
It runs fine and you don't get any warnings, but the output may not be what one
expects:
hi there
ARRAY(0x1a7f018)hi there
That's because the first argument is an array ref that gets stringified! In your
example, that's
likely to be caught quickly because this is stuff to be printed and therefore will
have an
immediate visual response for the programmer. However, if this is some obscure
subroutine that's
munging internal data, it will silently corrupt that data and this could be a nasty
bug to track
down.
There is one other problem I have with it. Many times, new Perl programmers ask why
the following
doesn't work:
while (<>) {
my $line = chomp;
# do more stuff here
}
That's because chomp acts directly on the variable in question (in this case, $_) and
returns the
number of characters that it chomped. There are a few functions in Perl that act
directly on the
variable, but these cause much confusion. In your routine above, I would return the
new data,
rather than directly changing the first argument passed to it.
Cheers,
Curtis "Ovid" Poe
=====
Senior Programmer
Onsite! Technology (http://www.onsitetech.com/)
"Ovid" on http://www.perlmonks.org/
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