There's a short and a long answer. The short answer is no.
(The reason is that the syntax is special cased. You cannot
make a user function with the same prototype.)
The long answer is, yes you can, provided you use IO::File
and use its print method. Then you can just
subclass IO::File, and mask the print method.
-- Abigail | [reply] |
Instead of overloading print, how about redirecting STDOUT with a tied filehandle? Try this:
#! /usr/bin/perl -w
package NumberedPrint;
use strict;
sub new
{
my $self = bless {}, shift;
$self;
}
sub TIEHANDLE
{
shift->new(@_);
}
{
my $printed_to_stdout = 0;
sub PRINT
{
shift;
print ORIGINAL_STDOUT ++$printed_to_stdout, ': ', @_;
}
sub PRINTF
{
shift;
print ORIGINAL_STDOUT ++$printed_to_stdout, ': ', sprintf(@_);
}
}
*ORIGINAL_STDOUT = *main::STDOUT;
tie *main::STDOUT, 'NumberedPrint';
package main;
print "Hello.\n";
print "Hello again.\n";
print "Hello a third time.\n";
print NumberedPrint::ORIGINAL_STDOUT "\nA line without a number.\n";
select NumberedPrint::ORIGINAL_STDOUT;
print "A lot of\n";
print "lines without\n";
print "any numbers.\n";
print "\n";
select STDOUT;
print "The final line.\n";
__END__
This is probably pretty fragile, but may do what you need. I found a similar technique in Lennart Borgman's Win32::ASP::Cgi module, and it seems to work pretty well there (albeit for a totally different purpose).
--Bill
| [reply] |
There's probably a way of overloading print (export to
CORE::GLOBAL?); there's an example in the
mod_perl guide for
overloading die. So you may be able to overload print, but
maybe not.
But why don't you just write a debug (or trace)
function that you can call. The debug function should print out
whatever message it's given, but only if the debug flag is set.
You could even make it OO, and make the debug flag a member
of the Trace object. Or whatever you want to call it. Then you can
do whatever you want in the debug method, including
printing out numbered messages, and also printing out
caller information, if you want. | [reply] |
I've used similar techniques in the past, but they are not very satisfying. Additionally, this would require me to locate all my debug statements and upgrade them to the new method. I was hoping to avoid that.
| [reply] |
__LINE__ is a global symbol that represents the current
line number of the script. This isn't exactly what
you're looking for, but it should help you out none the less.
print __LINE__, " some stuff with a line number\n";
you might also want to check out the function "caller", it can
give you the line number from which the current subroutine was called
/\/\averick | [reply]
[d/l] |
i'm pretty sure that print cannot be
overloaded. in the Perl Cookbook, recipe 12.11,
print is listed as one of the functions that cannot be
overloaded as of 5.004. it refers to the function keyword()
in toke.c for determining whether or not you can overload
a built-in function. looking at toke.c in 5.6, it looks as
if it is still not possible to overload
print. | [reply] |
After mucking around with this for a while, as well as having others muck around, we can't seem to come up with an easy way to overload print. If you are feeling ambitious, take a look at the code for Fatal.pm, which may help you. Also look at the archives for c.l.p.m(oderated|isc) and see if this has come up there. If you don't mind the first line not being numbered, you could always use $\ to do this. Interesting problem, hopefully I will have a tuit to muck with it this weekend. But, I believe that since 5.004 or something this is one of the functions that can't be overloaded.
Cheers,
KM | [reply] |