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Clan

Section: User Contributed Perl Documentation (3)
Updated: 2004-04-30
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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.


 

Index

NAME
SYNOPSIS
DESCRIPTION
Forcing a Stack Trace
BUGS

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