Reporting Errors and Warnings Like Built-Ins
Problem
You want to generate errors and warnings in your modules, but when
you use warn
or die
, the user
sees your own filename and line number. You’d like your
functions to act like built-ins and report messages from the
perspective of the user’s code not your own.
Solution
The standard
Carp module provides functions to do this. Use
carp
instead of warn
. Use
croak
(for a short message) and
confess
(for a long message) instead of
die
.
Discussion
Like built-ins, some of your module’s functions generate
warnings or errors if all doesn’t go well. Think about
sqrt
: when you pass it a negative number (and you
haven’t used the Math::Complex module), an exception is raised,
producing a message such as "Can't
take
sqrt
of
-3
at
/tmp/negroot
line
17"
, where /tmp/negroot is
the name of your own program. But if you write your own function that
die
s, perhaps like this:
sub even_only { my $n = shift; die "$n is not even" if $n & 1; # one way to test #.... }
then the message will say it’s coming from the file your
even_only
function was itself compiled in, rather
than from the file the user was in when they called your function.
That’s where the Carp module comes in handy. Instead of using
die
, use croak
instead:
use Carp; sub even_only { my $n = shift; croak "$n is not even" if $n % 2; # here's another #.... }
If you just want to complain about something, but have the message
report where in the user’s code the problem occurred, call
carp
instead of ...
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