Dancer::Exception - class for throwing and catching exceptions

       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.

perl v5.36.0                                       2023-02-10                             Dancer::Exception(3pm)

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

       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 workflowinterruption. Dancer users should
       ignore this feature.

   WhatitmeansforDancerusers
       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 Dancer::Exception::Base.

$Dancer::Exception::Verbose
       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.

try
       Same as in Try::Tiny

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

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

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

   raise
         # 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 raisingarguments 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 'Myexception'.

   register_exception
       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.

   registered_exceptions
         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.

       Dancer::Exception - class for throwing and catching exceptions

           use Dancer::Exception qw(:all);

           register_exception('DataProblem',
                               message_pattern => "test message : %s"
                             );

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

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

       version 1.3521