Manpages - Error.3pm

Error - Error/exception handling in an OO-ish way

version 0.17029

use Error qw(:try); throw Error::Simple( “A simple error”); sub xyz { … record Error::Simple(“A simple error”) and return; } unlink($file) or throw Error::Simple(“$file: $!”,$!); try { do_some_stuff(); die “error!” if $condition; throw Error::Simple “Oops!” if $other_condition; } catch Error::IO with { my $E = shift; print STDERR “File ”, $E->{-file}, “ had a problem\n”; } except { my $E = shift; my $general_handler=sub {send_message $E->{-description}}; return { UserException1 => $general_handler, UserException2 => $general_handler }; } otherwise { print STDERR “Well I dont know what to say\n”; } finally { close_the_garage_door_already(); # Should be reliable }; # Dont forget the trailing ; or you might be surprised

The Error package provides two interfaces. Firstly Error provides a procedural interface to exception handling. Secondly Error is a base class for errors/exceptions that can either be thrown, for subsequent catch, or can simply be recorded.

Errors in the class Error should not be thrown directly, but the user should throw errors from a sub-class of Error.

Using the Error module is no longer recommended due to the black-magical nature of its syntactic sugar, which often tends to break. Its maintainers have stopped actively writing code that uses it, and discourage people from doing so. See the SEE ALSO section below for better recommendations.

Error exports subroutines to perform exception handling. These will be exported if the :try tag is used in the use line.

try BLOCK CLAUSES

try is the main subroutine called by the user. All other subroutines exported are clauses to the try subroutine. The BLOCK will be evaluated and, if no error is throw, try will return the result of the block. CLAUSES are the subroutines below, which describe what to do in the event of an error being thrown within BLOCK.

catch CLASS with BLOCK

This clauses will cause all errors that satisfy $err->isa(CLASS) to be caught and handled by evaluating BLOCK. BLOCK will be passed two arguments. The first will be the error being thrown. The second is a reference to a scalar variable. If this variable is set by the catch block then, on return from the catch block, try will continue processing as if the catch block was never found. The error will also be available in $@. To propagate the error the catch block may call $err->throw If the scalar reference by the second argument is not set, and the error is not thrown. Then the current try block will return with the result from the catch block.

except BLOCK

When try is looking for a handler, if an except clause is found BLOCK is evaluated. The return value from this block should be a HASHREF or a list of key-value pairs, where the keys are class names and the values are CODE references for the handler of errors of that type.

otherwise BLOCK

Catch any error by executing the code in BLOCK When evaluated BLOCK will be passed one argument, which will be the error being processed. The error will also be available in $@. Only one otherwise block may be specified per try block

finally BLOCK

Execute the code in BLOCK either after the code in the try block has successfully completed, or if the try block throws an error then BLOCK will be executed after the handler has completed. If the handler throws an error then the error will be caught, the finally block will be executed and the error will be re-thrown. Only one finally block may be specified per try block

Moose exports a keyword called with which clashes with Error’s. This example returns a prototype mismatch error:

package MyTest; use warnings; use Moose; use Error qw(:try);

(Thanks to maik.hentsche@amd.com for the report.).

This variable holds a reference to a subroutine that converts errors that are plain strings to objects. It is used by Error.pm to convert textual errors to objects, and can be overridden by the user.

It accepts a single argument which is a hash reference to named parameters. Currently the only named parameter passed is text which is the text of the error, but others may be available in the future.

For example the following code will cause Error.pm to throw objects of the class MyError::Bar by default:

sub throw_MyError_Bar { my $args = shift; my $err = MyError::Bar->new(); $err->{MyBarText} = $args->{text}; return $err; } { local $Error::ObjectifyCallback = \&throw_MyError_Bar; # Error handling here. }

Error also provides handlers to extend the output of the warn() perl function, and to handle the printing of a thrown Error that is not caught or otherwise handled. These are not installed by default, but are requested using the :warndie tag in the use line.

use Error qw( :warndie );

These new error handlers are installed in $SIG{_ _WARN_ _} and $SIG{_ _DIE_ _}. If these handlers are already defined when the tag is imported, the old values are stored, and used during the new code. Thus, to arrange for custom handling of warnings and errors, you will need to perform something like the following:

BEGIN { $SIG{_ WARN } = sub { print STDERR “My special warning handler: $[0]“ }; } use Error qw( :warndie );

Note that setting $SIG{_ _WARN_ _} after the :warndie tag has been imported will overwrite the handler that Error provides. If this cannot be avoided, then the tag can be explicitly =import=ed later

use Error; $SIG{_ WARN _} = …; import Error qw( :warndie );

See Exception::Class for a different module providing Object-Oriented exception handling, along with a convenient syntax for declaring hierarchies for them. It doesn’t provide Error’s syntactic sugar of try { ... }, catch { ... }, etc. which may be a good thing or a bad thing based on what you want. (Because Error’s syntactic sugar tends to break.)

Error::Exception aims to combine Error and Exception::Class with correct stringification.

TryCatch and Try::Tiny are similar in concept to Error.pm only providing a syntax that hopefully breaks less.

None, but that does not mean there are not any.

Graham Barr <gbarr@pobox.com>

The code that inspired me to write this was originally written by Peter Seibel <peter@weblogic.com> and adapted by Jesse Glick <jglick@sig.bsh.com>.

:warndie handlers added by Paul Evans <leonerd@leonerd.org.uk>

Shlomi Fish, http://www.shlomifish.org/ .

Arun Kumar U <u_arunkumar@yahoo.com>

Copyright (c) 1997-8 Graham Barr. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

Shlomi Fish ( http://www.shlomifish.org/ )

Please report any bugs or feature requests on the bugtracker website https://github.com/shlomif/perl-error.pm/issues

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.

This software is copyright (c) 2020 by Shlomi Fish ( http://www.shlomifish.org/ ).

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