Clan.pod   [plain text]

=head1 NAME

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 "C<>" from Perl 5.005_03. It has been
modified to skip all package names matching the pattern given in
the "use" statement inside the "C<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 "C<Carp::Clan qw(^Pack::);>"
(or at least the one in which the error or warning gets raised).

Thus when for example your script "" 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 "" where
"Pack::A" was called, and not in "Pack::A" where "Pack::B" was called,
as the unmodified "C<>" would try to make you believe C<:-)>.

This works similarly if "Pack::B" calls "Pack::C" where the
exception is raised, etcetera.

In other words, this blames all errors in the "C<Pack::*>" modules
on the user of these modules, i.e., on you. C<;-)>

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 C<@ISA>
- as in the original "C<>" 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 "C<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 "C<use Carp;>" for C<;-)>),
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 "C<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.

=head2 Forcing a Stack Trace

As a debugging aid, you can force "C<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 "C<$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 "C<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.

=head1 BUGS

The "C<Carp::Clan>" routines don't handle exception objects currently.
If called with a first argument that is a reference, they simply
call "C<die()>" or "C<warn()>", as appropriate.