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Carp::Clan - Report errors from perspective of caller of a ``clan'' of modules
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!";
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.
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.
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.