autodie::exception(3perl)        Perl Programmers Reference Guide       autodie::exception(3perl)



NAME
       autodie::exception - Exceptions from autodying functions.

SYNOPSIS
           eval {
               use autodie;

               open(my $fh, '<', 'some_file.txt');

               ...
           };

           if (my $E = $@) {
               say "Ooops!  ",$E->caller," had problems: $@";
           }

DESCRIPTION
       When an autodie enabled function fails, it generates an "autodie::exception" object.  This
       can be interrogated to determine further information about the error that occurred.

       This document is broken into two sections; those methods that are most useful to the end-
       developer, and those methods for anyone wishing to subclass or get very familiar with
       "autodie::exception".

   Common Methods
       These methods are intended to be used in the everyday dealing of exceptions.

       The following assume that the error has been copied into a separate scalar:

           if ($E = $@) {
               ...
           }

       This is not required, but is recommended in case any code is called which may reset or
       alter $@.

       args

           my $array_ref = $E->args;

       Provides a reference to the arguments passed to the subroutine that died.

       function

           my $sub = $E->function;

       The subroutine (including package) that threw the exception.

       file

           my $file = $E->file;

       The file in which the error occurred (eg, "myscript.pl" or "MyTest.pm").

       package

           my $package = $E->package;

       The package from which the exceptional subroutine was called.

       caller

           my $caller = $E->caller;

       The subroutine that called the exceptional code.

       line

           my $line = $E->line;

       The line in "$E->file" where the exceptional code was called.

       context

           my $context = $E->context;

       The context in which the subroutine was called by autodie; usually the same as the context
       in which you called the autodying subroutine.  This can be 'list', 'scalar', or undefined
       (unknown).  It will never be 'void', as "autodie" always captures the return value in one
       way or another.

       For some core functions that always return a scalar value regardless of their context (eg,
       "chown"), this may be 'scalar', even if you used a list context.

       return

           my $return_value = $E->return;

       The value(s) returned by the failed subroutine.  When the subroutine was called in a list
       context, this will always be a reference to an array containing the results.  When the
       subroutine was called in a scalar context, this will be the actual scalar returned.

       errno

           my $errno = $E->errno;

       The value of $! at the time when the exception occurred.

       NOTE: This method will leave the main "autodie::exception" class and become part of a role
       in the future.  You should only call "errno" for exceptions where $! would reasonably have
       been set on failure.

       eval_error

           my $old_eval_error = $E->eval_error;

       The contents of $@ immediately after autodie triggered an exception.  This may be useful
       when dealing with modules such as Text::Balanced that set (but do not throw) $@ on error.

       matches

           if ( $e->matches('open') ) { ... }

           if ( $e ~~ 'open' ) { ... }

       "matches" is used to determine whether a given exception matches a particular role.  On
       Perl 5.10, using smart-match ("~~") with an "autodie::exception" object will use "matches"
       underneath.

       An exception is considered to match a string if:

       ·   For a string not starting with a colon, the string exactly matches the package and
           subroutine that threw the exception.  For example, "MyModule::log".  If the string
           does not contain a package name, "CORE::" is assumed.

       ·   For a string that does start with a colon, if the subroutine throwing the exception
           does that behaviour.  For example, the "CORE::open" subroutine does ":file", ":io" and
           ":all".

           See "CATEGORIES" in autodie for further information.

   Advanced methods
       The following methods, while usable from anywhere, are primarily intended for developers
       wishing to subclass "autodie::exception", write code that registers custom error messages,
       or otherwise work closely with the "autodie::exception" model.

       register

           autodie::exception->register( 'CORE::open' => \&mysub );

       The "register" method allows for the registration of a message handler for a given
       subroutine.  The full subroutine name including the package should be used.

       Registered message handlers will receive the "autodie::exception" object as the first
       parameter.

       add_file_and_line

           say "Problem occurred",$@->add_file_and_line;

       Returns the string " at %s line %d", where %s is replaced with the filename, and %d is
       replaced with the line number.

       Primarily intended for use by format handlers.

       stringify

           say "The error was: ",$@->stringify;

       Formats the error as a human readable string.  Usually there's no reason to call this
       directly, as it is used automatically if an "autodie::exception" object is ever used as a
       string.

       Child classes can override this method to change how they're stringified.

       format_default

           my $error_string = $E->format_default;

       This produces the default error string for the given exception, without using any
       registered message handlers.  It is primarily intended to be called from a message handler
       when they have been passed an exception they don't want to format.

       Child classes can override this method to change how default messages are formatted.

       new

           my $error = autodie::exception->new(
               args => \@_,
               function => "CORE::open",
               errno => $!,
               context => 'scalar',
               return => undef,
           );

       Creates a new "autodie::exception" object.  Normally called directly from an autodying
       function.  The "function" argument is required, its the function we were trying to call
       that generated the exception.  The "args" parameter is optional.

       The "errno" value is optional.  In versions of "autodie::exception" 1.99 and earlier the
       code would try to automatically use the current value of $!, but this was unreliable and
       is no longer supported.

       Atrributes such as package, file, and caller are determined automatically, and cannot be
       specified.

SEE ALSO
       autodie, autodie::exception::system

LICENSE
       Copyright (C)2008 Paul Fenwick

       This is free software.  You may modify and/or redistribute this code under the same terms
       as Perl 5.10 itself, or, at your option, any later version of Perl 5.

AUTHOR
       Paul Fenwick <pjf AT perltraining.au>



perl v5.20.2                                2014-12-27                  autodie::exception(3perl)