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Report errors from perspective of caller of a "clan" of modules

Carp::Clan - Report errors from perspective of caller of a "clan" of modules


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 ``'' 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 ``'' 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 ``'' 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 ``'' 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.


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.