perl / FromCPAN / Error.pmon commit Merge branch 'jk/am-i-resolved-fix' into maint (5bbbd57)
   1# Error.pm
   2#
   3# Copyright (c) 1997-8 Graham Barr <gbarr@ti.com>. All rights reserved.
   4# This program is free software; you can redistribute it and/or
   5# modify it under the same terms as Perl itself.
   6#
   7# Based on my original Error.pm, and Exceptions.pm by Peter Seibel
   8# <peter@weblogic.com> and adapted by Jesse Glick <jglick@sig.bsh.com>.
   9#
  10# but modified ***significantly***
  11
  12package Error;
  13
  14use strict;
  15use warnings;
  16
  17use vars qw($VERSION);
  18use 5.004;
  19
  20$VERSION = "0.17025";
  21
  22use overload (
  23        '""'       =>   'stringify',
  24        '0+'       =>   'value',
  25        'bool'     =>   sub { return 1; },
  26        'fallback' =>   1
  27);
  28
  29$Error::Depth = 0;      # Depth to pass to caller()
  30$Error::Debug = 0;      # Generate verbose stack traces
  31@Error::STACK = ();     # Clause stack for try
  32$Error::THROWN = undef; # last error thrown, a workaround until die $ref works
  33
  34my $LAST;               # Last error created
  35my %ERROR;              # Last error associated with package
  36
  37sub _throw_Error_Simple
  38{
  39    my $args = shift;
  40    return Error::Simple->new($args->{'text'});
  41}
  42
  43$Error::ObjectifyCallback = \&_throw_Error_Simple;
  44
  45
  46# Exported subs are defined in Error::subs
  47
  48use Scalar::Util ();
  49
  50sub import {
  51    shift;
  52    my @tags = @_;
  53    local $Exporter::ExportLevel = $Exporter::ExportLevel + 1;
  54
  55    @tags = grep {
  56       if( $_ eq ':warndie' ) {
  57          Error::WarnDie->import();
  58          0;
  59       }
  60       else {
  61          1;
  62       }
  63    } @tags;
  64
  65    Error::subs->import(@tags);
  66}
  67
  68# I really want to use last for the name of this method, but it is a keyword
  69# which prevent the syntax  last Error
  70
  71sub prior {
  72    shift; # ignore
  73
  74    return $LAST unless @_;
  75
  76    my $pkg = shift;
  77    return exists $ERROR{$pkg} ? $ERROR{$pkg} : undef
  78        unless ref($pkg);
  79
  80    my $obj = $pkg;
  81    my $err = undef;
  82    if($obj->isa('HASH')) {
  83        $err = $obj->{'__Error__'}
  84            if exists $obj->{'__Error__'};
  85    }
  86    elsif($obj->isa('GLOB')) {
  87        $err = ${*$obj}{'__Error__'}
  88            if exists ${*$obj}{'__Error__'};
  89    }
  90
  91    $err;
  92}
  93
  94sub flush {
  95    shift; #ignore
  96
  97    unless (@_) {
  98       $LAST = undef;
  99       return;
 100    }
 101
 102    my $pkg = shift;
 103    return unless ref($pkg);
 104
 105    undef $ERROR{$pkg} if defined $ERROR{$pkg};
 106}
 107
 108# Return as much information as possible about where the error
 109# happened. The -stacktrace element only exists if $Error::DEBUG
 110# was set when the error was created
 111
 112sub stacktrace {
 113    my $self = shift;
 114
 115    return $self->{'-stacktrace'}
 116        if exists $self->{'-stacktrace'};
 117
 118    my $text = exists $self->{'-text'} ? $self->{'-text'} : "Died";
 119
 120    $text .= sprintf(" at %s line %d.\n", $self->file, $self->line)
 121        unless($text =~ /\n$/s);
 122
 123    $text;
 124}
 125
 126
 127sub associate {
 128    my $err = shift;
 129    my $obj = shift;
 130
 131    return unless ref($obj);
 132
 133    if($obj->isa('HASH')) {
 134        $obj->{'__Error__'} = $err;
 135    }
 136    elsif($obj->isa('GLOB')) {
 137        ${*$obj}{'__Error__'} = $err;
 138    }
 139    $obj = ref($obj);
 140    $ERROR{ ref($obj) } = $err;
 141
 142    return;
 143}
 144
 145
 146sub new {
 147    my $self = shift;
 148    my($pkg,$file,$line) = caller($Error::Depth);
 149
 150    my $err = bless {
 151        '-package' => $pkg,
 152        '-file'    => $file,
 153        '-line'    => $line,
 154        @_
 155    }, $self;
 156
 157    $err->associate($err->{'-object'})
 158        if(exists $err->{'-object'});
 159
 160    # To always create a stacktrace would be very inefficient, so
 161    # we only do it if $Error::Debug is set
 162
 163    if($Error::Debug) {
 164        require Carp;
 165        local $Carp::CarpLevel = $Error::Depth;
 166        my $text = defined($err->{'-text'}) ? $err->{'-text'} : "Error";
 167        my $trace = Carp::longmess($text);
 168        # Remove try calls from the trace
 169        $trace =~ s/(\n\s+\S+__ANON__[^\n]+)?\n\s+eval[^\n]+\n\s+Error::subs::try[^\n]+(?=\n)//sog;
 170        $trace =~ s/(\n\s+\S+__ANON__[^\n]+)?\n\s+eval[^\n]+\n\s+Error::subs::run_clauses[^\n]+\n\s+Error::subs::try[^\n]+(?=\n)//sog;
 171        $err->{'-stacktrace'} = $trace
 172    }
 173
 174    $@ = $LAST = $ERROR{$pkg} = $err;
 175}
 176
 177# Throw an error. this contains some very gory code.
 178
 179sub throw {
 180    my $self = shift;
 181    local $Error::Depth = $Error::Depth + 1;
 182
 183    # if we are not rethrow-ing then create the object to throw
 184    $self = $self->new(@_) unless ref($self);
 185
 186    die $Error::THROWN = $self;
 187}
 188
 189# syntactic sugar for
 190#
 191#    die with Error( ... );
 192
 193sub with {
 194    my $self = shift;
 195    local $Error::Depth = $Error::Depth + 1;
 196
 197    $self->new(@_);
 198}
 199
 200# syntactic sugar for
 201#
 202#    record Error( ... ) and return;
 203
 204sub record {
 205    my $self = shift;
 206    local $Error::Depth = $Error::Depth + 1;
 207
 208    $self->new(@_);
 209}
 210
 211# catch clause for
 212#
 213# try { ... } catch CLASS with { ... }
 214
 215sub catch {
 216    my $pkg = shift;
 217    my $code = shift;
 218    my $clauses = shift || {};
 219    my $catch = $clauses->{'catch'} ||= [];
 220
 221    unshift @$catch,  $pkg, $code;
 222
 223    $clauses;
 224}
 225
 226# Object query methods
 227
 228sub object {
 229    my $self = shift;
 230    exists $self->{'-object'} ? $self->{'-object'} : undef;
 231}
 232
 233sub file {
 234    my $self = shift;
 235    exists $self->{'-file'} ? $self->{'-file'} : undef;
 236}
 237
 238sub line {
 239    my $self = shift;
 240    exists $self->{'-line'} ? $self->{'-line'} : undef;
 241}
 242
 243sub text {
 244    my $self = shift;
 245    exists $self->{'-text'} ? $self->{'-text'} : undef;
 246}
 247
 248# overload methods
 249
 250sub stringify {
 251    my $self = shift;
 252    defined $self->{'-text'} ? $self->{'-text'} : "Died";
 253}
 254
 255sub value {
 256    my $self = shift;
 257    exists $self->{'-value'} ? $self->{'-value'} : undef;
 258}
 259
 260package Error::Simple;
 261
 262use vars qw($VERSION);
 263
 264$VERSION = "0.17025";
 265
 266@Error::Simple::ISA = qw(Error);
 267
 268sub new {
 269    my $self  = shift;
 270    my $text  = "" . shift;
 271    my $value = shift;
 272    my(@args) = ();
 273
 274    local $Error::Depth = $Error::Depth + 1;
 275
 276    @args = ( -file => $1, -line => $2)
 277        if($text =~ s/\s+at\s+(\S+)\s+line\s+(\d+)(?:,\s*<[^>]*>\s+line\s+\d+)?\.?\n?$//s);
 278    push(@args, '-value', 0 + $value)
 279        if defined($value);
 280
 281    $self->SUPER::new(-text => $text, @args);
 282}
 283
 284sub stringify {
 285    my $self = shift;
 286    my $text = $self->SUPER::stringify;
 287    $text .= sprintf(" at %s line %d.\n", $self->file, $self->line)
 288        unless($text =~ /\n$/s);
 289    $text;
 290}
 291
 292##########################################################################
 293##########################################################################
 294
 295# Inspired by code from Jesse Glick <jglick@sig.bsh.com> and
 296# Peter Seibel <peter@weblogic.com>
 297
 298package Error::subs;
 299
 300use Exporter ();
 301use vars qw(@EXPORT_OK @ISA %EXPORT_TAGS);
 302
 303@EXPORT_OK   = qw(try with finally except otherwise);
 304%EXPORT_TAGS = (try => \@EXPORT_OK);
 305
 306@ISA = qw(Exporter);
 307
 308sub run_clauses ($$$\@) {
 309    my($clauses,$err,$wantarray,$result) = @_;
 310    my $code = undef;
 311
 312    $err = $Error::ObjectifyCallback->({'text' =>$err}) unless ref($err);
 313
 314    CATCH: {
 315
 316        # catch
 317        my $catch;
 318        if(defined($catch = $clauses->{'catch'})) {
 319            my $i = 0;
 320
 321            CATCHLOOP:
 322            for( ; $i < @$catch ; $i += 2) {
 323                my $pkg = $catch->[$i];
 324                unless(defined $pkg) {
 325                    #except
 326                    splice(@$catch,$i,2,$catch->[$i+1]->($err));
 327                    $i -= 2;
 328                    next CATCHLOOP;
 329                }
 330                elsif(Scalar::Util::blessed($err) && $err->isa($pkg)) {
 331                    $code = $catch->[$i+1];
 332                    while(1) {
 333                        my $more = 0;
 334                        local($Error::THROWN, $@);
 335                        my $ok = eval {
 336                            $@ = $err;
 337                            if($wantarray) {
 338                                @{$result} = $code->($err,\$more);
 339                            }
 340                            elsif(defined($wantarray)) {
 341                                @{$result} = ();
 342                                $result->[0] = $code->($err,\$more);
 343                            }
 344                            else {
 345                                $code->($err,\$more);
 346                            }
 347                            1;
 348                        };
 349                        if( $ok ) {
 350                            next CATCHLOOP if $more;
 351                            undef $err;
 352                        }
 353                        else {
 354                            $err = $@ || $Error::THROWN;
 355                                $err = $Error::ObjectifyCallback->({'text' =>$err})
 356                                        unless ref($err);
 357                        }
 358                        last CATCH;
 359                    };
 360                }
 361            }
 362        }
 363
 364        # otherwise
 365        my $owise;
 366        if(defined($owise = $clauses->{'otherwise'})) {
 367            my $code = $clauses->{'otherwise'};
 368            my $more = 0;
 369        local($Error::THROWN, $@);
 370            my $ok = eval {
 371                $@ = $err;
 372                if($wantarray) {
 373                    @{$result} = $code->($err,\$more);
 374                }
 375                elsif(defined($wantarray)) {
 376                    @{$result} = ();
 377                    $result->[0] = $code->($err,\$more);
 378                }
 379                else {
 380                    $code->($err,\$more);
 381                }
 382                1;
 383            };
 384            if( $ok ) {
 385                undef $err;
 386            }
 387            else {
 388                $err = $@ || $Error::THROWN;
 389
 390                $err = $Error::ObjectifyCallback->({'text' =>$err})
 391                        unless ref($err);
 392            }
 393        }
 394    }
 395    $err;
 396}
 397
 398sub try (&;$) {
 399    my $try = shift;
 400    my $clauses = @_ ? shift : {};
 401    my $ok = 0;
 402    my $err = undef;
 403    my @result = ();
 404
 405    unshift @Error::STACK, $clauses;
 406
 407    my $wantarray = wantarray();
 408
 409    do {
 410        local $Error::THROWN = undef;
 411        local $@ = undef;
 412
 413        $ok = eval {
 414            if($wantarray) {
 415                @result = $try->();
 416            }
 417            elsif(defined $wantarray) {
 418                $result[0] = $try->();
 419            }
 420            else {
 421                $try->();
 422            }
 423            1;
 424        };
 425
 426        $err = $@ || $Error::THROWN
 427            unless $ok;
 428    };
 429
 430    shift @Error::STACK;
 431
 432    $err = run_clauses($clauses,$err,wantarray,@result)
 433    unless($ok);
 434
 435    $clauses->{'finally'}->()
 436        if(defined($clauses->{'finally'}));
 437
 438    if (defined($err))
 439    {
 440        if (Scalar::Util::blessed($err) && $err->can('throw'))
 441        {
 442            throw $err;
 443        }
 444        else
 445        {
 446            die $err;
 447        }
 448    }
 449
 450    wantarray ? @result : $result[0];
 451}
 452
 453# Each clause adds a sub to the list of clauses. The finally clause is
 454# always the last, and the otherwise clause is always added just before
 455# the finally clause.
 456#
 457# All clauses, except the finally clause, add a sub which takes one argument
 458# this argument will be the error being thrown. The sub will return a code ref
 459# if that clause can handle that error, otherwise undef is returned.
 460#
 461# The otherwise clause adds a sub which unconditionally returns the users
 462# code reference, this is why it is forced to be last.
 463#
 464# The catch clause is defined in Error.pm, as the syntax causes it to
 465# be called as a method
 466
 467sub with (&;$) {
 468    @_
 469}
 470
 471sub finally (&) {
 472    my $code = shift;
 473    my $clauses = { 'finally' => $code };
 474    $clauses;
 475}
 476
 477# The except clause is a block which returns a hashref or a list of
 478# key-value pairs, where the keys are the classes and the values are subs.
 479
 480sub except (&;$) {
 481    my $code = shift;
 482    my $clauses = shift || {};
 483    my $catch = $clauses->{'catch'} ||= [];
 484
 485    my $sub = sub {
 486        my $ref;
 487        my(@array) = $code->($_[0]);
 488        if(@array == 1 && ref($array[0])) {
 489            $ref = $array[0];
 490            $ref = [ %$ref ]
 491                if(UNIVERSAL::isa($ref,'HASH'));
 492        }
 493        else {
 494            $ref = \@array;
 495        }
 496        @$ref
 497    };
 498
 499    unshift @{$catch}, undef, $sub;
 500
 501    $clauses;
 502}
 503
 504sub otherwise (&;$) {
 505    my $code = shift;
 506    my $clauses = shift || {};
 507
 508    if(exists $clauses->{'otherwise'}) {
 509        require Carp;
 510        Carp::croak("Multiple otherwise clauses");
 511    }
 512
 513    $clauses->{'otherwise'} = $code;
 514
 515    $clauses;
 516}
 517
 5181;
 519
 520package Error::WarnDie;
 521
 522sub gen_callstack($)
 523{
 524    my ( $start ) = @_;
 525
 526    require Carp;
 527    local $Carp::CarpLevel = $start;
 528    my $trace = Carp::longmess("");
 529    # Remove try calls from the trace
 530    $trace =~ s/(\n\s+\S+__ANON__[^\n]+)?\n\s+eval[^\n]+\n\s+Error::subs::try[^\n]+(?=\n)//sog;
 531    $trace =~ s/(\n\s+\S+__ANON__[^\n]+)?\n\s+eval[^\n]+\n\s+Error::subs::run_clauses[^\n]+\n\s+Error::subs::try[^\n]+(?=\n)//sog;
 532    my @callstack = split( m/\n/, $trace );
 533    return @callstack;
 534}
 535
 536my $old_DIE;
 537my $old_WARN;
 538
 539sub DEATH
 540{
 541    my ( $e ) = @_;
 542
 543    local $SIG{__DIE__} = $old_DIE if( defined $old_DIE );
 544
 545    die @_ if $^S;
 546
 547    my ( $etype, $message, $location, @callstack );
 548    if ( ref($e) && $e->isa( "Error" ) ) {
 549        $etype = "exception of type " . ref( $e );
 550        $message = $e->text;
 551        $location = $e->file . ":" . $e->line;
 552        @callstack = split( m/\n/, $e->stacktrace );
 553    }
 554    else {
 555        # Don't apply subsequent layer of message formatting
 556        die $e if( $e =~ m/^\nUnhandled perl error caught at toplevel:\n\n/ );
 557        $etype = "perl error";
 558        my $stackdepth = 0;
 559        while( caller( $stackdepth ) =~ m/^Error(?:$|::)/ ) {
 560            $stackdepth++
 561        }
 562
 563        @callstack = gen_callstack( $stackdepth + 1 );
 564
 565        $message = "$e";
 566        chomp $message;
 567
 568        if ( $message =~ s/ at (.*?) line (\d+)\.$// ) {
 569            $location = $1 . ":" . $2;
 570        }
 571        else {
 572            my @caller = caller( $stackdepth );
 573            $location = $caller[1] . ":" . $caller[2];
 574        }
 575    }
 576
 577    shift @callstack;
 578    # Do it this way in case there are no elements; we don't print a spurious \n
 579    my $callstack = join( "", map { "$_\n"} @callstack );
 580
 581    die "\nUnhandled $etype caught at toplevel:\n\n  $message\n\nThrown from: $location\n\nFull stack trace:\n\n$callstack\n";
 582}
 583
 584sub TAXES
 585{
 586    my ( $message ) = @_;
 587
 588    local $SIG{__WARN__} = $old_WARN if( defined $old_WARN );
 589
 590    $message =~ s/ at .*? line \d+\.$//;
 591    chomp $message;
 592
 593    my @callstack = gen_callstack( 1 );
 594    my $location = shift @callstack;
 595
 596    # $location already starts in a leading space
 597    $message .= $location;
 598
 599    # Do it this way in case there are no elements; we don't print a spurious \n
 600    my $callstack = join( "", map { "$_\n"} @callstack );
 601
 602    warn "$message:\n$callstack";
 603}
 604
 605sub import
 606{
 607    $old_DIE  = $SIG{__DIE__};
 608    $old_WARN = $SIG{__WARN__};
 609
 610    $SIG{__DIE__}  = \&DEATH;
 611    $SIG{__WARN__} = \&TAXES;
 612}
 613
 6141;
 615
 616__END__
 617
 618=head1 NAME
 619
 620Error - Error/exception handling in an OO-ish way
 621
 622=head1 WARNING
 623
 624Using the "Error" module is B<no longer recommended> due to the black-magical
 625nature of its syntactic sugar, which often tends to break. Its maintainers
 626have stopped actively writing code that uses it, and discourage people
 627from doing so. See the "SEE ALSO" section below for better recommendations.
 628
 629=head1 SYNOPSIS
 630
 631    use Error qw(:try);
 632
 633    throw Error::Simple( "A simple error");
 634
 635    sub xyz {
 636        ...
 637        record Error::Simple("A simple error")
 638            and return;
 639    }
 640
 641    unlink($file) or throw Error::Simple("$file: $!",$!);
 642
 643    try {
 644        do_some_stuff();
 645        die "error!" if $condition;
 646        throw Error::Simple "Oops!" if $other_condition;
 647    }
 648    catch Error::IO with {
 649        my $E = shift;
 650        print STDERR "File ", $E->{'-file'}, " had a problem\n";
 651    }
 652    except {
 653        my $E = shift;
 654        my $general_handler=sub {send_message $E->{-description}};
 655        return {
 656            UserException1 => $general_handler,
 657            UserException2 => $general_handler
 658        };
 659    }
 660    otherwise {
 661        print STDERR "Well I don't know what to say\n";
 662    }
 663    finally {
 664        close_the_garage_door_already(); # Should be reliable
 665    }; # Don't forget the trailing ; or you might be surprised
 666
 667=head1 DESCRIPTION
 668
 669The C<Error> package provides two interfaces. Firstly C<Error> provides
 670a procedural interface to exception handling. Secondly C<Error> is a
 671base class for errors/exceptions that can either be thrown, for
 672subsequent catch, or can simply be recorded.
 673
 674Errors in the class C<Error> should not be thrown directly, but the
 675user should throw errors from a sub-class of C<Error>.
 676
 677=head1 PROCEDURAL INTERFACE
 678
 679C<Error> exports subroutines to perform exception handling. These will
 680be exported if the C<:try> tag is used in the C<use> line.
 681
 682=over 4
 683
 684=item try BLOCK CLAUSES
 685
 686C<try> is the main subroutine called by the user. All other subroutines
 687exported are clauses to the try subroutine.
 688
 689The BLOCK will be evaluated and, if no error is throw, try will return
 690the result of the block.
 691
 692C<CLAUSES> are the subroutines below, which describe what to do in the
 693event of an error being thrown within BLOCK.
 694
 695=item catch CLASS with BLOCK
 696
 697This clauses will cause all errors that satisfy C<$err-E<gt>isa(CLASS)>
 698to be caught and handled by evaluating C<BLOCK>.
 699
 700C<BLOCK> will be passed two arguments. The first will be the error
 701being thrown. The second is a reference to a scalar variable. If this
 702variable is set by the catch block then, on return from the catch
 703block, try will continue processing as if the catch block was never
 704found. The error will also be available in C<$@>.
 705
 706To propagate the error the catch block may call C<$err-E<gt>throw>
 707
 708If the scalar reference by the second argument is not set, and the
 709error is not thrown. Then the current try block will return with the
 710result from the catch block.
 711
 712=item except BLOCK
 713
 714When C<try> is looking for a handler, if an except clause is found
 715C<BLOCK> is evaluated. The return value from this block should be a
 716HASHREF or a list of key-value pairs, where the keys are class names
 717and the values are CODE references for the handler of errors of that
 718type.
 719
 720=item otherwise BLOCK
 721
 722Catch any error by executing the code in C<BLOCK>
 723
 724When evaluated C<BLOCK> will be passed one argument, which will be the
 725error being processed. The error will also be available in C<$@>.
 726
 727Only one otherwise block may be specified per try block
 728
 729=item finally BLOCK
 730
 731Execute the code in C<BLOCK> either after the code in the try block has
 732successfully completed, or if the try block throws an error then
 733C<BLOCK> will be executed after the handler has completed.
 734
 735If the handler throws an error then the error will be caught, the
 736finally block will be executed and the error will be re-thrown.
 737
 738Only one finally block may be specified per try block
 739
 740=back
 741
 742=head1 COMPATIBILITY
 743
 744L<Moose> exports a keyword called C<with> which clashes with Error's. This
 745example returns a prototype mismatch error:
 746
 747    package MyTest;
 748
 749    use warnings;
 750    use Moose;
 751    use Error qw(:try);
 752
 753(Thanks to C<maik.hentsche@amd.com> for the report.).
 754
 755=head1 CLASS INTERFACE
 756
 757=head2 CONSTRUCTORS
 758
 759The C<Error> object is implemented as a HASH. This HASH is initialized
 760with the arguments that are passed to it's constructor. The elements
 761that are used by, or are retrievable by the C<Error> class are listed
 762below, other classes may add to these.
 763
 764        -file
 765        -line
 766        -text
 767        -value
 768        -object
 769
 770If C<-file> or C<-line> are not specified in the constructor arguments
 771then these will be initialized with the file name and line number where
 772the constructor was called from.
 773
 774If the error is associated with an object then the object should be
 775passed as the C<-object> argument. This will allow the C<Error> package
 776to associate the error with the object.
 777
 778The C<Error> package remembers the last error created, and also the
 779last error associated with a package. This could either be the last
 780error created by a sub in that package, or the last error which passed
 781an object blessed into that package as the C<-object> argument.
 782
 783=over 4
 784
 785=item Error->new()
 786
 787See the Error::Simple documentation.
 788
 789=item throw ( [ ARGS ] )
 790
 791Create a new C<Error> object and throw an error, which will be caught
 792by a surrounding C<try> block, if there is one. Otherwise it will cause
 793the program to exit.
 794
 795C<throw> may also be called on an existing error to re-throw it.
 796
 797=item with ( [ ARGS ] )
 798
 799Create a new C<Error> object and returns it. This is defined for
 800syntactic sugar, eg
 801
 802    die with Some::Error ( ... );
 803
 804=item record ( [ ARGS ] )
 805
 806Create a new C<Error> object and returns it. This is defined for
 807syntactic sugar, eg
 808
 809    record Some::Error ( ... )
 810        and return;
 811
 812=back
 813
 814=head2 STATIC METHODS
 815
 816=over 4
 817
 818=item prior ( [ PACKAGE ] )
 819
 820Return the last error created, or the last error associated with
 821C<PACKAGE>
 822
 823=item flush ( [ PACKAGE ] )
 824
 825Flush the last error created, or the last error associated with
 826C<PACKAGE>.It is necessary to clear the error stack before exiting the
 827package or uncaught errors generated using C<record> will be reported.
 828
 829     $Error->flush;
 830
 831=cut
 832
 833=back
 834
 835=head2 OBJECT METHODS
 836
 837=over 4
 838
 839=item stacktrace
 840
 841If the variable C<$Error::Debug> was non-zero when the error was
 842created, then C<stacktrace> returns a string created by calling
 843C<Carp::longmess>. If the variable was zero the C<stacktrace> returns
 844the text of the error appended with the filename and line number of
 845where the error was created, providing the text does not end with a
 846newline.
 847
 848=item object
 849
 850The object this error was associated with
 851
 852=item file
 853
 854The file where the constructor of this error was called from
 855
 856=item line
 857
 858The line where the constructor of this error was called from
 859
 860=item text
 861
 862The text of the error
 863
 864=item $err->associate($obj)
 865
 866Associates an error with an object to allow error propagation. I.e:
 867
 868    $ber->encode(...) or
 869        return Error->prior($ber)->associate($ldap);
 870
 871=back
 872
 873=head2 OVERLOAD METHODS
 874
 875=over 4
 876
 877=item stringify
 878
 879A method that converts the object into a string. This method may simply
 880return the same as the C<text> method, or it may append more
 881information. For example the file name and line number.
 882
 883By default this method returns the C<-text> argument that was passed to
 884the constructor, or the string C<"Died"> if none was given.
 885
 886=item value
 887
 888A method that will return a value that can be associated with the
 889error. For example if an error was created due to the failure of a
 890system call, then this may return the numeric value of C<$!> at the
 891time.
 892
 893By default this method returns the C<-value> argument that was passed
 894to the constructor.
 895
 896=back
 897
 898=head1 PRE-DEFINED ERROR CLASSES
 899
 900=head2 Error::Simple
 901
 902This class can be used to hold simple error strings and values. It's
 903constructor takes two arguments. The first is a text value, the second
 904is a numeric value. These values are what will be returned by the
 905overload methods.
 906
 907If the text value ends with C<at file line 1> as $@ strings do, then
 908this information will be used to set the C<-file> and C<-line> arguments
 909of the error object.
 910
 911This class is used internally if an eval'd block die's with an error
 912that is a plain string. (Unless C<$Error::ObjectifyCallback> is modified)
 913
 914
 915=head1 $Error::ObjectifyCallback
 916
 917This variable holds a reference to a subroutine that converts errors that
 918are plain strings to objects. It is used by Error.pm to convert textual
 919errors to objects, and can be overridden by the user.
 920
 921It accepts a single argument which is a hash reference to named parameters.
 922Currently the only named parameter passed is C<'text'> which is the text
 923of the error, but others may be available in the future.
 924
 925For example the following code will cause Error.pm to throw objects of the
 926class MyError::Bar by default:
 927
 928    sub throw_MyError_Bar
 929    {
 930        my $args = shift;
 931        my $err = MyError::Bar->new();
 932        $err->{'MyBarText'} = $args->{'text'};
 933        return $err;
 934    }
 935
 936    {
 937        local $Error::ObjectifyCallback = \&throw_MyError_Bar;
 938
 939        # Error handling here.
 940    }
 941
 942=cut
 943
 944=head1 MESSAGE HANDLERS
 945
 946C<Error> also provides handlers to extend the output of the C<warn()> perl
 947function, and to handle the printing of a thrown C<Error> that is not caught
 948or otherwise handled. These are not installed by default, but are requested
 949using the C<:warndie> tag in the C<use> line.
 950
 951 use Error qw( :warndie );
 952
 953These new error handlers are installed in C<$SIG{__WARN__}> and
 954C<$SIG{__DIE__}>. If these handlers are already defined when the tag is
 955imported, the old values are stored, and used during the new code. Thus, to
 956arrange for custom handling of warnings and errors, you will need to perform
 957something like the following:
 958
 959 BEGIN {
 960   $SIG{__WARN__} = sub {
 961     print STDERR "My special warning handler: $_[0]"
 962   };
 963 }
 964
 965 use Error qw( :warndie );
 966
 967Note that setting C<$SIG{__WARN__}> after the C<:warndie> tag has been
 968imported will overwrite the handler that C<Error> provides. If this cannot be
 969avoided, then the tag can be explicitly C<import>ed later
 970
 971 use Error;
 972
 973 $SIG{__WARN__} = ...;
 974
 975 import Error qw( :warndie );
 976
 977=head2 EXAMPLE
 978
 979The C<__DIE__> handler turns messages such as
 980
 981 Can't call method "foo" on an undefined value at examples/warndie.pl line 16.
 982
 983into
 984
 985 Unhandled perl error caught at toplevel:
 986
 987   Can't call method "foo" on an undefined value
 988
 989 Thrown from: examples/warndie.pl:16
 990
 991 Full stack trace:
 992
 993         main::inner('undef') called at examples/warndie.pl line 20
 994         main::outer('undef') called at examples/warndie.pl line 23
 995
 996=cut
 997
 998=head1 SEE ALSO
 999
1000See L<Exception::Class> for a different module providing Object-Oriented
1001exception handling, along with a convenient syntax for declaring hierarchies
1002for them. It doesn't provide Error's syntactic sugar of C<try { ... }>,
1003C<catch { ... }>, etc. which may be a good thing or a bad thing based
1004on what you want. (Because Error's syntactic sugar tends to break.)
1005
1006L<Error::Exception> aims to combine L<Error> and L<Exception::Class>
1007"with correct stringification".
1008
1009L<TryCatch> and L<Try::Tiny> are similar in concept to Error.pm only providing
1010a syntax that hopefully breaks less.
1011
1012=head1 KNOWN BUGS
1013
1014None, but that does not mean there are not any.
1015
1016=head1 AUTHORS
1017
1018Graham Barr <gbarr@pobox.com>
1019
1020The code that inspired me to write this was originally written by
1021Peter Seibel <peter@weblogic.com> and adapted by Jesse Glick
1022<jglick@sig.bsh.com>.
1023
1024C<:warndie> handlers added by Paul Evans <leonerd@leonerd.org.uk>
1025
1026=head1 MAINTAINER
1027
1028Shlomi Fish, L<http://www.shlomifish.org/> .
1029
1030=head1 PAST MAINTAINERS
1031
1032Arun Kumar U <u_arunkumar@yahoo.com>
1033
1034=head1 COPYRIGHT
1035
1036Copyright (c) 1997-8  Graham Barr. All rights reserved.
1037This program is free software; you can redistribute it and/or modify it
1038under the same terms as Perl itself.
1039
1040=cut