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.\" ========================================================================
.\"
.IX Title "Carp::Clan 3"
.TH Carp::Clan 3 "2009-10-24" "perl v5.8.7" "User Contributed Perl Documentation"
.SH "NAME"
Carp::Clan \- Report errors from perspective of caller of a "clan" of modules
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& carp    \- warn of errors (from perspective of caller)
.Ve
.PP
.Vb 1
\& cluck   \- warn of errors with stack backtrace
.Ve
.PP
.Vb 1
\& croak   \- die of errors (from perspective of caller)
.Ve
.PP
.Vb 1
\& confess \- die of errors with stack backtrace
.Ve
.PP
.Vb 2
\&    use Carp::Clan qw(^MyClan::);
\&    croak "We're outta here!";
.Ve
.PP
.Vb 2
\&    use Carp::Clan;
\&    confess "This is how we got here!";
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This module is based on "\f(CW\*(C`Carp.pm\*(C'\fR\*(L" from Perl 5.005_03. It has been
modified to skip all package names matching the pattern given in
the \*(R"use\*(L" statement inside the \*(R"\f(CW\*(C`qw()\*(C'\fR" term (or argument list).
.PP
Suppose you have a family of modules or classes named \*(L"Pack::A\*(R",
\&\*(L"Pack::B\*(R" and so on, and each of them uses "\f(CW\*(C`Carp::Clan qw(^Pack::);\*(C'\fR"
(or at least the one in which the error or warning gets raised).
.PP
Thus when for example your script \*(L"tool.pl\*(R" calls module \*(L"Pack::A\*(R",
and module \*(L"Pack::A\*(R" calls module \*(L"Pack::B\*(R", an exception raised in
module \*(L"Pack::B\*(R" will appear to have originated in \*(L"tool.pl\*(R" where
\&\*(L"Pack::A\*(R" was called, and not in \*(L"Pack::A\*(R" where \*(L"Pack::B\*(R" was called,
as the unmodified "\f(CW\*(C`Carp.pm\*(C'\fR" would try to make you believe \f(CW\*(C`:\-)\*(C'\fR.
.PP
This works similarly if \*(L"Pack::B\*(R" calls \*(L"Pack::C\*(R" where the
exception is raised, etcetera.
.PP
In other words, this blames all errors in the "\f(CW\*(C`Pack::*\*(C'\fR" modules
on the user of these modules, i.e., on you. \f(CW\*(C`;\-)\*(C'\fR
.PP
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 \f(CW@ISA\fR
\&\- as in the original "\f(CW\*(C`Carp.pm\*(C'\fR" module \- doesn't help).
.PP
The purpose and advantage of this is that a \*(L"clan\*(R" 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.
.PP
In case you just want to ward off all error messages from the module
in which you "\f(CW\*(C`use Carp::Clan\*(C'\fR\*(L", 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 \*(R"\f(CW\*(C`use Carp;\*(C'\fR" for \f(CW\*(C`;\-)\*(C'\fR),
instead of in your module itself (which is what you can do with a
\&\*(L"die\*(R" or \*(L"warn\*(R" anyway), you do not need to provide a pattern,
the module will automatically provide the correct one for you.
.PP
I.e., just "\f(CW\*(C`use Carp::Clan;\*(C'\fR\*(L" without any arguments and call \*(R"carp\*(L"
or \*(R"croak" as appropriate, and they will automatically defend your
module against all blames!
.PP
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.
.Sh "Forcing a Stack Trace"
.IX Subsection "Forcing a Stack Trace"
As a debugging aid, you can force "\f(CW\*(C`Carp::Clan\*(C'\fR\*(L" to treat a \*(R"croak\*(L" as
a \*(R"confess\*(L" and a \*(R"carp\*(L" as a \*(R"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.
.PP
This feature is enabled either by \*(L"importing\*(R" the non-existent symbol
\&'verbose', or by setting the global variable "\f(CW$Carp::Clan::Verbose\fR"
to a true value.
.PP
You would typically enable it by saying
.PP
.Vb 1
\&    use Carp::Clan qw(verbose);
.Ve
.PP
Note that you can both specify a \*(L"family pattern\*(R" and the string \*(L"verbose\*(R"
inside the "\f(CW\*(C`qw()\*(C'\fR\*(L" term (or argument list) of the \*(R"use\*(L" statement, but
consider that a pattern of packages to skip is pointless when \*(R"verbose"
causes a full stack trace anyway.
.SH "BUGS"
.IX Header "BUGS"
The "\f(CW\*(C`Carp::Clan\*(C'\fR\*(L" routines don't handle exception objects currently.
If called with a first argument that is a reference, they simply
call \*(R"\f(CW\*(C`die()\*(C'\fR\*(L" or \*(R"\f(CW\*(C`warn()\*(C'\fR", as appropriate.