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Clan(3)                              User Contributed Perl Documentation                             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 v5.8.8                                      2004-04-30                                          Clan(3)