what does (caller 1)[3] in Perl

[Pawan Sangal]

Hi,

I've a code. I am unable to understand below code. Can anyone help me in understanding the belwo code. What the (caller 1)[3] means in below code.

package CD::Music;
use strict;
use Carp;

sub read_only
{
croak "Can't change value of read only attribute".(caller 1)[3] if @_ > 1;
}

#read only accessors
sub name { &read_only; $_[0]->{_name} }
sub artist { &read_only; $_[0]->{_artist} }
sub publisher { &read_only; $_[0]->{_publisher} }
sub ISBN { &read_only; $_[0]->{_ISBN} }

#read write accessors
sub last_played
{
my ($self, $when) = @_;
$self->{_played} = $when if @_ > 1;
$self->{_played};
}

sub rating
{
my ($self, $rating) = @_;
$self->{_rating} = $rating if @_ > 1;
$self->{_rating};
}

Suppose all the above read only accessors are called, then what will be the output of read_only subroutine each time, it is called. I just want to know the output by (caller 1)[3]. I am not familiar with this term.

Is caller 1 is printing the calling function's name or something else....please help....I'll appreciate your help..in this regard.

Thanks & Regards
Pawan Sangal

[wje_lf]

Do this at the command prompt:

man perlfunc

and you will get documentation on every Perl function, including caller. I just looked, and caller's in there.

If that man page is not installed on your system, you can google for this:

man perlfunc Linux

instead.

Hope this helps.

[Pawan Sangal]

Do this at the command prompt:

man perlfunc

and you will get documentation on every Perl function, including caller. I just looked, and caller's in there.

If that man page is not installed on your system, you can google for this:

man perlfunc Linux

instead.

Hope this helps.

Thanks Bill.......

[Pawan Sangal]

Hi Bill,

I think I have got the meaning of the (caller 1)[3] in above program.

Actually, the (caller 1)[3] will give us the name of the calling subroutine.

I read little theory on caller, and found the use of caller function. Every time Perl calls a subroutine, details of that subroutine are stored in a stack, which is for Perl's internal use.

When caller called on scalar context:
$package = caller; #only the package name is retreived

When caller called on list context:
($package, $file, $line) = caller; #retreives the package, filename, line of the current subroutine

It's same writing:
($package, $file, $line) = caller;
-- or --
($package, $file, $line) = caller 1;

Since, @caller = caller 0; #will return whole information about the calling subroutine. around 10 items.

Hence, to know the calling subroutine's name in a program can be written in two ways:
($package, $file, $line, $subrout) = caller 1; print "$subrout\n";
-- or --
$subrout = (caller 1)[3]; print "$subrout\n";