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 unmod
ified ""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 mod
ules 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 auto
matically 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 nonexistent symbol 'verbose', or by setting the global vari
able "$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 ref
erence, they simply call ""die()"" or ""warn()"", as
appropriate.