Dancer::Exception(3pm) User Contributed Perl Documentation Dancer::Exception(3pm)
NAME
Dancer::Exception - class for throwing and catching exceptions
SYNOPSIS
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 {
$exception->rethrow
}
};
DESCRIPTION
Dancer::Exception is based on Try::Tiny. You can try and catch exceptions, like in Try::Tiny.
Exceptions are objects, from subclasses of Dancer::Exception::Base.
However, for internal Dancer usage, we introduce a special class of exceptions, called Dancer::Continuation. Exceptions that are from this
class are not caught with a "catch" block, but only with a "continuation". That's a cheap way to implement a workflow interruption. Dancer
users should ignore this feature.
What it means for Dancer users
Users can throw and catch exceptions, using "try" and "catch". They can reuse some Dancer core exceptions ("Dancer::Exception::Base::*"),
but they can also create new exception classes, and use them for their own means. That way it's easy to use custom exceptions in a Dancer
application. Have a look at "register_exception", "raise", and the methods in Dancer::Exception::Base.
METHODS
try
Same as in Try::Tiny
catch
Same as in Try::Tiny. The exception can be retrieved as the first parameter:
try { ... } catch { my ($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 $username is unknown";
raise provides an easy way to throw an exception. First parameter is the name of the exception class, without the "Dancer::Exception::"
prefix. other parameters are stored as raising arguments in the exception. Usually the parameters is an exception message, but it's left to
the exception class implementation.
If the exception class name starts with a "+", then the "Dancer::Exception::" won't be added. This allows one to build their own exception
class hierarchy, but you should first look at "register_exception" before implementing your own class hierarchy. If you really wish to
build your own exception class hierarchy, we recommend that all exceptions inherit of Dancer::Exception::. Or at least it should implement
its methods.
The exception class can also be written as words separated by underscores, it'll be camelized automatically. So 'Exception::Foo' and
'exception_foo' are equivalent. Be careful, 'MyException' can't be written 'myexception', as it would be camelized into 'Myexception'.
register_exception
This method allows one to register custom exceptions, usable by Dancer users in their route code (actually pretty much everywhere).
# simple exception
register_exception ('InvalidCredentials',
message_pattern => "invalid credentials : %s",
);
This registers a new custom exception. To use it, do:
raise InvalidCredentials => "user Herbert not found";
The exception message can be retrieved with the "$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.
GLOBAL VARIABLE
$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.
perl v5.14.2 2012-03-31 Dancer::Exception(3pm)