Provided by: libdancer-perl_1.3500+dfsg-1_all bug


       Dancer::Exception - class for throwing and catching exceptions


       version 1.3500


           use Dancer::Exception qw(:all);

                               message_pattern => "test message : %s"

           sub do_stuff {
             raise DataProblem => "we've lost data!";

           try {
           } catch {
             # an exception was thrown
             my ($exception) = @_;
             if ($exception->does('DataProblem')) {
               # handle the data problem
               my $message = $exception->message();
             } else {


       Dancer::Exception is based on Try::Tiny. You can try and catch exceptions, like in

       Exceptions are objects, from subclasses of Dancer::Exception::Base.

       However, for internal Dancer usage, we introduce a special class of exceptions, called
       Dancer::Continuation. Exceptions that are from this class are not caught with a "catch"
       block, but only with a "continuation". That's a cheap way to implement a workflow
       interruption. Dancer users should ignore this feature.

   What it means for Dancer users
       Users can throw and catch exceptions, using "try" and "catch". They can reuse some Dancer
       core exceptions ("Dancer::Exception::Base::*"), but they can also create new exception
       classes, and use them for their own means. That way it's easy to use custom exceptions in
       a Dancer application. Have a look at "register_exception", "raise", and the methods in


       Same as in Try::Tiny

       Same as in Try::Tiny. The exception can be retrieved as the first parameter:

           try { ... } catch { my ($exception) = @_; };

       To be used by Dancer developers only, in Dancer core code.

         # raise Dancer::Exception::Base::Custom
         raise Custom => "user $username is unknown";

         # raise Dancer::Exception::Base::Custom::Frontend
         raise 'Custom::Frontend' => "user $username is unknown";

         # same, raise Dancer::Exception::Base::Custom::Frontend
         raise custom_frontend => "user $username is unknown";

         # raise My::Own::ExceptionSystem::Invalid::Login
         raise '+My::Own::ExceptionSystem::Invalid::Login' => "user $username is unknown";

       raise provides an easy way to throw an exception. First parameter is the name of the
       exception class, without the "Dancer::Exception::" prefix. other parameters are stored as
       raising arguments in the exception. Usually the parameters is an exception message, but
       it's left to the exception class implementation.

       If the exception class name starts with a "+", then the "Dancer::Exception::" won't be
       added. This allows one to build their own exception class hierarchy, but you should first
       look at "register_exception" before implementing your own class hierarchy. If you really
       wish to build your own exception class hierarchy, we recommend that all exceptions inherit
       of Dancer::Exception::. Or at least it should implement its methods.

       The exception class can also be written as words separated by underscores, it'll be
       camelized automatically. So 'Exception::Foo' and 'exception_foo' are equivalent. Be
       careful, 'MyException' can't be written 'myexception', as it would be camelized into

       This method allows one to register custom exceptions, usable by Dancer users in their
       route code (actually pretty much everywhere).

         # simple exception
         register_exception ('InvalidCredentials',
                             message_pattern => "invalid credentials : %s",

       This registers a new custom exception. To use it, do:

         raise InvalidCredentials => "user Herbert not found";

       The exception message can be retrieved with the "$exception->message" method, and we'll be
       "invalid credentials : user Herbert not found" (see methods in Dancer::Exception::Base)

         # complex exception
         register_exception ('InvalidLogin',
                             composed_from => [qw(Fatal InvalidCredentials)],
                             message_pattern => "wrong login or password",

       In this example, the "InvalidLogin" is built as a composition of the "Fatal" and
       "InvalidCredentials" exceptions. See the "does" method in Dancer::Exception::Base.

         my @exception_classes = registered_exceptions;

       Returns the list of exception class names. It will list core exceptions "and" custom
       exceptions (except the one you've registered with a leading "+", see
       "register_exception"). The list is sorted.


       When set to 1, exceptions will stringify with a long stack trace. This variable is similar
       to $Carp::Verbose. I recommend you use it like that:

         local $Dancer::Exception::Verbose;
         $Dancer::Exception::Verbose = 1;

       All the Carp global variables can also be used to alter the stacktrace generation.


       Dancer Core Developers


       This software is copyright (c) 2010 by Alexis Sukrieh.

       This is free software; you can redistribute it and/or modify it under the same terms as
       the Perl 5 programming language system itself.