Carp::Clan(3) User Contributed Perl Documentation Carp::Clan(3)
NAME
Carp::Clan - Report errors from perspective of caller of a "clan" of modules
SYNOPSIS
carp - warn of errors (from perspective of caller)
cluck - warn of errors with stack backtrace
croak - die of errors (from perspective of caller)
confess - die of errors with stack backtrace
use Carp::Clan qw(^MyClan::);
croak "We're outta here!";
use Carp::Clan;
confess "This is how we got here!";
DESCRIPTION
This module is based on ""Carp.pm"" from Perl 5.005_03. It has been modified to skip all package names matching the pattern given in the
"use" statement inside the ""qw()"" term (or argument list).
Suppose you have a family of modules or classes named "Pack::A", "Pack::B" and so on, and each of them uses ""Carp::Clan qw(^Pack::);"" (or
at least the one in which the error or warning gets raised).
Thus when for example your script "tool.pl" calls module "Pack::A", and module "Pack::A" calls module "Pack::B", an exception raised in
module "Pack::B" will appear to have originated in "tool.pl" where "Pack::A" was called, and not in "Pack::A" where "Pack::B" was called,
as the unmodified ""Carp.pm"" would try to make you believe ":-)".
This works similarly if "Pack::B" calls "Pack::C" where the exception is raised, etcetera.
In other words, this blames all errors in the ""Pack::*"" modules on the user of these modules, i.e., on you. ";-)"
The skipping of a clan (or family) of packages according to a pattern describing its members is necessary in cases where these modules are
not classes derived from each other (and thus when examining @ISA - as in the original ""Carp.pm"" module - doesn't help).
The purpose and advantage of this is that a "clan" of modules can work together (and call each other) and throw exceptions at various
depths down the calling hierarchy and still appear as a monolithic block (as though they were a single module) from the perspective of the
caller.
In case you just want to ward off all error messages from the module in which you ""use Carp::Clan"", i.e., if you want to make all error
messages or warnings to appear to originate from where your module was called (this is what you usually used to ""use Carp;"" for ";-)"),
instead of in your module itself (which is what you can do with a "die" or "warn" anyway), you do not need to provide a pattern, the module
will automatically provide the correct one for you.
I.e., just ""use Carp::Clan;"" without any arguments and call "carp" or "croak" as appropriate, and they will automatically defend your
module against all blames!
In other words, a pattern is only necessary if you want to make several modules (more than one) work together and appear as though they
were only one.
Forcing a Stack Trace
As a debugging aid, you can force ""Carp::Clan"" to treat a "croak" as a "confess" and a "carp" as a "cluck". In other words, force a
detailed stack trace to be given. This can be very helpful when trying to understand why, or from where, a warning or error is being
generated.
This feature is enabled either by "importing" the non-existent symbol 'verbose', or by setting the global variable "$Carp::Clan::Verbose"
to a true value.
You would typically enable it by saying
use Carp::Clan qw(verbose);
Note that you can both specify a "family pattern" and the string "verbose" inside the ""qw()"" term (or argument list) of the "use"
statement, but consider that a pattern of packages to skip is pointless when "verbose" causes a full stack trace anyway.
BUGS
The ""Carp::Clan"" routines don't handle exception objects currently. If called with a first argument that is a reference, they simply
call ""die()"" or ""warn()"", as appropriate.
perl v5.16.2 2009-10-24 Carp::Clan(3)