Exception::Class::Base
Section: User Contributed Perl Documentation (3)
Updated: 2021-01-27
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NAME
Exception::Class::Base - A base class for exception objects
VERSION
version 1.44
SYNOPSIS
use Exception::Class 'MyException';
eval { MyException->throw( error => 'I feel funny.' ) };
print $@->error;
DESCRIPTION
This class is the base class for all exceptions created by
Exception::Class. It provides a number of methods for getting information
about the exception.
METHODS
MyException->Trace($boolean)
Each
"Exception::Class::Base" subclass can be set individually to include a
stacktrace when the
"as_string" method is called. The default is to not
include a stacktrace. Calling this method with a value changes this
behavior. It always returns the current value (after any change is applied).
This value is inherited by any subclasses. However, if this value is set for a
subclass, it will thereafter be independent of the value in
"Exception::Class::Base".
Do not call this on the "Exception::Class::Base" class directly or you'll
change it for all exception classes that use Exception::Class, including
ones created in modules you don't control.
This is a class method, not an object method.
MyException->UnsafeRefCapture($boolean)
When a
"Devel::StackTrace" object is created, it walks through the stack and
stores the arguments which were passed to each subroutine on the stack. If any
of these arguments are references, then that means that the
"Devel::StackTrace" ends up increasing the ref count of these references,
delaying their destruction.
Since "Exception::Class::Base" uses "Devel::StackTrace" internally, this
method provides a way to tell "Devel::StackTrace" not to store these
references. Instead, "Devel::StackTrace" replaces references with their
stringified representation.
This method defaults to false. As with "Trace", it is inherited by subclasses
but setting it in a subclass makes it independent thereafter.
Do not call this on the "Exception::Class::Base" class directly or you'll
change it for all exception classes that use Exception::Class, including
ones created in modules you don't control.
MyException->RespectOverload($boolean)
When a
"Devel::StackTrace" object stringifies, by default it ignores
stringification overloading on any objects being dealt with.
Since "Exception::Class::Base" uses "Devel::StackTrace" internally, this
method provides a way to tell "Devel::StackTrace" to respect overloading.
This method defaults to false. As with "Trace", it is inherited by subclasses
but setting it in a subclass makes it independent thereafter.
Do not call this on the "Exception::Class::Base" class directly or you'll
change it for all exception classes that use Exception::Class, including
ones created in modules you don't control.
MyException->MaxArgLength($boolean)
When a
"Devel::StackTrace" object stringifies, by default it displays the
full argument for each function. This parameter can be used to limit the
maximum length of each argument.
Since "Exception::Class::Base" uses "Devel::StackTrace" internally, this
method provides a way to tell "Devel::StackTrace" to limit the length of
arguments.
This method defaults to 0. As with "Trace", it is inherited by subclasses but
setting it in a subclass makes it independent thereafter.
Do not call this on the "Exception::Class::Base" class directly or you'll
change it for all exception classes that use Exception::Class, including
ones created in modules you don't control.
MyException->Fields
This method returns the extra fields defined for the given class, as a list.
Do not call this on the "Exception::Class::Base" class directly or you'll
change it for all exception classes that use Exception::Class, including
ones created in modules you don't control.
MyException->throw( $message )
MyException->throw( message => $message )
MyException->throw( error => $error )
This method creates a new object with the given error message. If no error
message is given, this will be an empty string. It then dies with this object
as its argument.
This method also takes a "show_trace" parameter which indicates whether or
not the particular exception object being created should show a stacktrace
when its "as_string" method is called. This overrides the value of "Trace"
for this class if it is given.
The frames included in the trace can be controlled by the "ignore_class" and
"ignore_package" parameters. These are passed directly to Devel::Stacktrace's
constructor. See "Devel::Stacktrace" for more details. This class always
passes "__PACKAGE__" for "ignore_class" and 'Exception::Class' for
"ignore_package", in addition to any arguments you provide.
If only a single value is given to the constructor it is assumed to be the
message parameter.
Additional keys corresponding to the fields defined for the particular
exception subclass will also be accepted.
MyException->new(...)
This method takes the same parameters as
"throw", but instead of dying simply
returns a new exception object.
This method is always called when constructing a new exception object via the
"throw" method.
MyException->description
Returns the description for the given
"Exception::Class::Base" subclass. The
"Exception::Class::Base" class's description is ``Generic exception'' (this may
change in the future). This is also an object method.
$exception->rethrow
Simply dies with the object as its sole argument. It's just syntactic
sugar. This does not change any of the object's attribute values. However, it
will cause
"caller" to report the die as coming from within the
"Exception::Class::Base" class rather than where rethrow was called.
Of course, you always have access to the original stacktrace for the exception
object.
$exception->message
$exception->error
Returns the error/message associated with the exception.
$exception->pid
Returns the pid at the time the exception was thrown.
$exception->uid
Returns the real user id at the time the exception was thrown.
$exception->gid
Returns the real group id at the time the exception was thrown.
$exception->euid
Returns the effective user id at the time the exception was thrown.
$exception->egid
Returns the effective group id at the time the exception was thrown.
$exception->time
Returns the time in seconds since the epoch at the time the exception was
thrown.
$exception->package
Returns the package from which the exception was thrown.
$exception->file
Returns the file within which the exception was thrown.
$exception->line
Returns the line where the exception was thrown.
$exception->context_hash
Returns a hash reference with the following keys:
- •
-
time
- •
-
pid
- •
-
uid
- •
-
euid
- •
-
gid
- •
-
egid
$exception->field_hash
Returns a hash reference where the keys are any fields defined for the
exception class and the values are the values associated with the field in the
given object.
$exception->trace
Returns the trace object associated with the object.
$exception->show_trace($boolean)
This method can be used to set whether or not a stack trace is included when
the as_string method is called or the object is stringified.
$exception->as_string
Returns a string form of the error message (something like what you'd expect
from die). If the class or object is set to show traces then then the full
trace is also included. The result looks like
"Carp::confess".
$exception->full_message
Called by the
"as_string" method to get the message. By default, this is the
same as calling the
"message" method, but may be overridden by a
subclass. See below for details.
LIGHTWEIGHT EXCEPTIONS
A lightweight exception is one which records no information about its context
when it is created. This can be achieved by setting
"$class->NoContextInfo" to a true value.
You can make this the default for a class of exceptions by setting it after
creating the class:
use Exception::Class (
'LightWeight',
'HeavyWeight',
);
LightWeight->NoContextInfo(1);
A lightweight exception does have a stack trace object, nor does it record the
time, pid, uid, euid, gid, or egid. It only has a message.
OVERLOADING
"Exception::Class::Base" objects are overloaded so that stringification
produces a normal error message. This just calls the
"$exception->as_string" method described above. This means that you can just
"print $@" after an
"eval" and not worry about whether or not its an actual object. It also means
an application or module could do this:
$SIG{__DIE__} = sub { Exception::Class::Base->throw( error => join '', @_ ); };
and this would probably not break anything (unless someone was expecting a
different type of exception object from "die").
OVERRIDING THE as_string METHOD
By default, the
"as_string" method simply returns the value
"message" or
"error" param plus a stack trace, if the class's
"Trace" method returns a
true value or
"show_trace" was set when creating the exception.
However, once you add new fields to a subclass, you may want to include those
fields in the stringified error.
Inside the "as_string" method, the message (non-stack trace) portion of the
error is generated by calling the "full_message" method. This can be easily
overridden. For example:
sub full_message {
my $self = shift;
my $msg = $self->message;
$msg .= " and foo was " . $self->foo;
return $msg;
}
SUPPORT
Bugs may be submitted at <
https://github.com/houseabsolute/Exception-Class/issues>.
I am also usually active on IRC as 'autarch' on "irc://irc.perl.org".
SOURCE
The source code repository for Exception-Class can be found at <
https://github.com/houseabsolute/Exception-Class>.
AUTHOR
Dave Rolsky <
autarch@urth.org>
COPYRIGHT AND LICENSE
This software is copyright (c) 2017 by Dave Rolsky.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
The full text of the license can be found in the
LICENSE file included with this distribution.