Carp::Clan(3pm)                User Contributed Perl Documentation                Carp::Clan(3pm)



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 v5.10.1                                2009-10-24                            Carp::Clan(3pm)