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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 v5.10.0                      2006-10-02                     Carp::Clan(3)

Mac OS X 10.6 - Generated Thu Sep 17 20:11:11 CDT 2009
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