phpman > man > Error(3pm)

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

VERSION
    version 0.17029

SYNOPSIS
        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 don't know what to say\n";
        }
        finally {
            close_the_garage_door_already(); # Should be reliable
        }; # Don't forget the trailing ; or you might be surprised

DESCRIPTION
    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".

WARNING
    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.

PROCEDURAL INTERFACE
    "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

COMPATIBILITY
    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 AT amd.com" for the report.).

CLASS INTERFACE
  CONSTRUCTORS
    The "Error" object is implemented as a HASH. This HASH is initialized with the arguments that
    are passed to it's constructor. The elements that are used by, or are retrievable by the "Error"
    class are listed below, other classes may add to these.

            -file
            -line
            -text
            -value
            -object

    If "-file" or "-line" are not specified in the constructor arguments then these will be
    initialized with the file name and line number where the constructor was called from.

    If the error is associated with an object then the object should be passed as the "-object"
    argument. This will allow the "Error" package to associate the error with the object.

    The "Error" package remembers the last error created, and also the last error associated with a
    package. This could either be the last error created by a sub in that package, or the last error
    which passed an object blessed into that package as the "-object" argument.

    Error->new()
        See the Error::Simple documentation.

    throw ( [ ARGS ] )
        Create a new "Error" object and throw an error, which will be caught by a surrounding "try"
        block, if there is one. Otherwise it will cause the program to exit.

        "throw" may also be called on an existing error to re-throw it.

    with ( [ ARGS ] )
        Create a new "Error" object and returns it. This is defined for syntactic sugar, eg

            die with Some::Error ( ... );

    record ( [ ARGS ] )
        Create a new "Error" object and returns it. This is defined for syntactic sugar, eg

            record Some::Error ( ... )
                and return;

  STATIC METHODS
    prior ( [ PACKAGE ] )
        Return the last error created, or the last error associated with "PACKAGE"

    flush ( [ PACKAGE ] )
        Flush the last error created, or the last error associated with "PACKAGE".It is necessary to
        clear the error stack before exiting the package or uncaught errors generated using "record"
        will be reported.

             $Error->flush;

  OBJECT METHODS
    stacktrace
        If the variable $Error::Debug was non-zero when the error was created, then "stacktrace"
        returns a string created by calling "Carp::longmess". If the variable was zero the
        "stacktrace" returns the text of the error appended with the filename and line number of
        where the error was created, providing the text does not end with a newline.

    object
        The object this error was associated with

    file
        The file where the constructor of this error was called from

    line
        The line where the constructor of this error was called from

    text
        The text of the error

    $err->associate($obj)
        Associates an error with an object to allow error propagation. I.e:

            $ber->encode(...) or
                return Error->prior($ber)->associate($ldap);

  OVERLOAD METHODS
    stringify
        A method that converts the object into a string. This method may simply return the same as
        the "text" method, or it may append more information. For example the file name and line
        number.

        By default this method returns the "-text" argument that was passed to the constructor, or
        the string "Died" if none was given.

    value
        A method that will return a value that can be associated with the error. For example if an
        error was created due to the failure of a system call, then this may return the numeric
        value of $! at the time.

        By default this method returns the "-value" argument that was passed to the constructor.

PRE-DEFINED ERROR CLASSES
  Error::Simple
    This class can be used to hold simple error strings and values. It's constructor takes two
    arguments. The first is a text value, the second is a numeric value. These values are what will
    be returned by the overload methods.

    If the text value ends with "at file line 1" as $@ strings do, then this information will be
    used to set the "-file" and "-line" arguments of the error object.

    This class is used internally if an eval'd block die's with an error that is a plain string.
    (Unless $Error::ObjectifyCallback is modified)

$Error::ObjectifyCallback
    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.
        }

MESSAGE HANDLERS
    "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 );

  EXAMPLE
    The "__DIE__" handler turns messages such as

     Can't call method "foo" on an undefined value at examples/warndie.pl line 16.

    into

     Unhandled perl error caught at toplevel:

       Can't call method "foo" on an undefined value

     Thrown from: examples/warndie.pl:16

     Full stack trace:

             main::inner('undef') called at examples/warndie.pl line 20
             main::outer('undef') called at examples/warndie.pl line 23

SEE ALSO
    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.

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

AUTHORS
    Graham Barr <gbarr AT pobox.com>

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

    ":warndie" handlers added by Paul Evans <leonerd AT leonerd.uk>

MAINTAINER
    Shlomi Fish, <http://www.shlomifish.org/> .

PAST MAINTAINERS
    Arun Kumar U <u_arunkumar AT yahoo.com>

COPYRIGHT
    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.

SUPPORT
  Websites
    The following websites have more information about this module, and may be of help to you. As
    always, in addition to those websites please use your favorite search engine to discover more
    resources.

    *   MetaCPAN

        A modern, open-source CPAN search engine, useful to view POD in HTML format.

        <https://metacpan.org/release/Error>

    *   Search CPAN

        The default CPAN search engine, useful to view POD in HTML format.

        <http://search.cpan.org/dist/Error>

    *   RT: CPAN's Bug Tracker

        The RT ( Request Tracker ) website is the default bug/issue tracking system for CPAN.

        <https://rt.cpan.org/Public/Dist/Display.html?Name=Error>

    *   CPAN Ratings

        The CPAN Ratings is a website that allows community ratings and reviews of Perl modules.

        <http://cpanratings.perl.org/d/Error>

    *   CPANTS

        The CPANTS is a website that analyzes the Kwalitee ( code metrics ) of a distribution.

        <http://cpants.cpanauthors.org/dist/Error>

    *   CPAN Testers

        The CPAN Testers is a network of smoke testers who run automated tests on uploaded CPAN
        distributions.

        <http://www.cpantesters.org/distro/E/Error>

    *   CPAN Testers Matrix

        The CPAN Testers Matrix is a website that provides a visual overview of the test results for
        a distribution on various Perls/platforms.

        <http://matrix.cpantesters.org/?dist=Error>

    *   CPAN Testers Dependencies

        The CPAN Testers Dependencies is a website that shows a chart of the test results of all
        dependencies for a distribution.

        <http://deps.cpantesters.org/?module=Error>

  Bugs / Feature Requests
    Please report any bugs or feature requests by email to "bug-error at rt.cpan.org", or through
    the web interface at <https://rt.cpan.org/Public/Bug/Report.html?Queue=Error>. You will be
    automatically notified of any progress on the request by the system.

  Source Code
    The code is open to the world, and available for you to hack on. Please feel free to browse it
    and play with it, or whatever. If you want to contribute patches, please send me a diff or prod
    me to pull from your repository :)

    <https://github.com/shlomif/perl-error.pm>

      git clone git://github.com/shlomif/perl-error.pm.git

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

BUGS
    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.

COPYRIGHT AND LICENSE
    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.