NAME

       custom::failures - Minimalist, customized exception hierarchy generator

VERSION

       version 0.003

SYNOPSIS

           package MyApp::failure;

           use custom::failures qw/io::file io::network/;

           # customize failure methodsX

DESCRIPTION

       This module works like failures but lets you define a customized exception hierarchy if
       you need a custom namespace, additional attributes, or customized object behaviors.

       Because failure classes have an @ISA chain and Perl by default uses depth-first-search to
       resolve method calls, you can override behavior anywhere in the custom hierarchy and it
       will take precedence over default "failure" behaviors.

       There are two methods that might be useful to override:

       •   message

       •   throw

       Both are described further, below.

USAGE

   Defining a custom failure hierarchy
           package MyApp::failure;

           use custom::failures qw/foo::bar/;

       This will define a failure class hierarchy under the calling package's namespace.  The
       following diagram show the classes that will be created (arrows denote 'is-a'
       relationships):

           MyApp::failure::foo::bar --> failure::foo::bar
                  |                        |
                  V                        V
           MyApp::failure::foo      --> failure::foo
                  |                        |
                  V                        V
           MyApp::failure           --> failure

       Alternatively, if you want a different namespace for the hierarchy, do it this way:

           use custom::failures 'MyApp::Error' => [ 'io::file' ];

       That will create the following classes and relationships:

           MyApp::Error::foo::bar --> failure::foo::bar
                  |                        |
                  V                        V
           MyApp::Error::foo      --> failure::foo
                  |                        |
                  V                        V
           MyApp::Error           --> failure

       By having custom classes also inherit from a standard namespace, you can throw a custom
       error class that will still be caught in the standard namespace:

           try {
               MyApp::failure::foo::bar->throw;
           }
           catch {
               if ( $_->$_isa( "failure::foo" ) ) {
                   # handle it here
               }
           };

   Adding custom attributes
       Failure classes are implemented with Class::Tiny, so adding attributes is trivially easy:

           package MyApp::failure;

           use custom::failures qw/foo::bar/;

           use Class::Tiny qw/user/;

       This adds a "user" attribute to "MyApp::failure" and all its subclasses so it can be set
       in the argument to "throw":

           MyApp::failure::foo->throw( { msg => "Ouch!", user => "me" } );

       Be sure to load "Class::Tiny" after you load "custom::failures" so that your @ISA is
       already set up.

   Overriding the "message" method
       Overriding "message" lets you modify how the error string is produced.  The "message"
       method takes a string (typically just the "msg" field) and returns a string.  It should
       not produce or append stack trace information.  That is done during object
       stringification.

       Call "SUPER::message" if you want the standard error text prepended ("Caught $class:
       ...").

       For example, if you want to use String::Flogger to render messages:

           package MyApp::failure;

           use custom::failures qw/foo::bar/;
           use String::Flogger qw/flog/;

           sub message {
               my ( $self, $msg ) = @_;
               return $self->SUPER::message( flog($msg) );
           }

       Then you can pass strings or array references or code references as the "msg" for "throw":

           MyApp::failure->throw( "just a string"               );
           MyApp::failure->throw( [ "show some data %s", $ref ] );
           MyApp::failure->throw( sub { call_expensive_sub() }  );

       Because the "message" method is only called during stringification (unless you call it
       yourself), the failure class type can be checked before any expensive rendering is done.

   Overriding the "throw" method
       Overriding "throw" lets you modify the arguments you can provide or ensure that a trace is
       included.  It can take whatever arguments you want and should call "SUPER::throw" with a
       hash reference to actually throw the error.

       For example, to capture the filename associated with file errors:

           package MyApp::failure;

           use custom::failures qw/file/;

           use Class::Tiny qw/filename/;

           sub throw {
               my ( $class, $msg, $file ) = @_;
               my $args = {
                   msg => $msg,
                   filename => $file,
                   trace => failures->croak_trace,
               };
               $self->SUPER::throw( $args );
           }

           sub message {
               # do something with 'msg' and 'filename'
           }

       Later you could use it like this:

           MyApp::failure::file->throw( opening => $some_file );

   Using BUILD
       "Class::Tiny" supports "BUILD", so you can also use that to do things with failure objects
       when thrown.  This example logs exceptions as they are built:

           use Log::Any qw/$log/;

           sub BUILD {
               my ($self) = @_;
               $log->error( $self->message );
           }

       By using "message" instead of stringifying $self, we log the message but not the trace (if
       any).

AUTHOR

       David Golden <dagolden@cpan.org>

COPYRIGHT AND LICENSE

       This software is Copyright (c) 2013 by David Golden.

       This is free software, licensed under:

         The Apache License, Version 2.0, January 2004