Class::Error(3)

NAME
Class::Error - Delayed checking of object failure

VERSION 2.41
Included in OOTools 2.41 distribution.

The latest versions changes are reported in the Changes file in this distribution.

The distribution includes:

•   Class::constr

    Pragma to implement constructor methods

•   Class::props

    Pragma to implement lvalue accessors with options

•   Class::groups

    Pragma to implement groups of properties accessors with options

•   Class::Error

    Delayed checking of object failure

•   Object::props

    Pragma to implement lvalue accessors with options

•   Object::groups

    Pragma to implement groups of properties accessors with options

•   Class::Util

    Class utility functions

INSTALLATION

Prerequisites
        Perl version >= 5.6.1

CPAN
        perl -MCPAN -e 'install OOTools'

Standard installation
    From the directory where this file is located, type:

        perl Makefile.PL
        make
        make test
        make install

SYNOPSIS
  package My::Package ;

  use Class::Error ;

  $undef_obj = Class::Error->new($error, $errnum)

  $undef_obj->any_method ;              # won't die and will return $undef_obj
  print 'is false' unless $undef_obj ;  # 'is false'
  print "$undef_obj" ;                  # '' with warning "Use of uninitialized
                                        # value in string..."
  print $undef_obj->any_method ;        # '' with same warning

  $empty_obj = Class::Error->new($error, $errnum, '')

  $empty_obj->any_method ;              # won't die and will return $empty_obj
  print 'is false' unless $empty_obj ;  # 'is false'
  print "$empty_obj" ;                  # '' no warnings
  print $empty_obj->any_method ;        # '' no warnings

DESCRIPTION
You can use this module to return a Class::Error object instead of a simple false value (e.g. when a sub or a property may return an object OR the undef value on failure).

That feature allows to check on the object itself, or delay the checking after calling any method on the object.

   $obj = AnyClass->new or die $obj->error
   AnyClass->new->any_method or die Class::Error->error  # static

For example, compare the difference between the behaviour of "obj_A" and "obj_B" if the "AnyClass->new" would return false:

   use Object::props
     ( { name    => 'obj_A',
         default => sub{ AnyClass->new or undef }
       },
       { name    => 'obj_B',
         default => sub{ AnyClass->new
                         or Class::Error->new('AnyClass->new failed') }
       }
     );

   # if AnyClass->new would fail (returning a false value)

   # this would die "Can't call method "any_method" on an undefined value..."
   $s->obj_A->any_method or do{ warn 'doing something else...';
                                do_something_else()
                              };
   # but this would execute the do{} block
   $s->obj_B->any_method or do{ warn 'doing something else...';
                                do_something_else()
                              };

METHODS

  AUTOLOAD
All the methods called on the Class::Error object (regardless the arguments) return a reference to the object itself, thus allowing you to call methods on methods:

   $error_obj->any_method('a', 'b')->any_other_method...

METHODS

  new ([ error [, errnum [, false]]] )
   $undef_obj = Class::Error->new($error, $errnum)       # undef
   $empty_obj = Class::Error->new($error, $errnum, '')   # empty
   $zero_obj  = Class::Error->new($error, $errnum, 0)    # 0

The constructor accepts 3 optional arguments and returns a Class::Error object.

error sets the error, which could be a simple string or any other value (also stored in $Class::Error::error), errnum sets the error number (also stored in $Class::Error::errnum) which you can retrieve with the "error" and "errnum" static or dynamic methods.

You can also pass a third argument (which must be false) to the new method or leave it undef: the scalar reference to the false argument will be used as the object value in any contexts (internally using "overload").

For example, if you leave the false argument as "undef", the Class::Error object itself is evaluated as undef in any contexts (e.g. false in boolean context like the undef value), but unlike the undef value, it is defined and allows you to call any methods on it.

Note: If you want to avoid the "use of uninitialized value..." warning when you use the object itself (or the result of its methods) in string context, you can pass an empty string to the constructor, or the 0 value for numeric context. Use that feature only if you know what you are doing, since a defined false value might make more difficult the debgging of real errors.

  error
Returns the last error string passed to the new() method:

   AnyClass->new->any_method or die Class::Error->error  # static
   $result = AnyClass->new->any_method or die $result->error
   $obj = AnyClass->new or die $obj->error

  errnum
Returns the last error number passed to the new() method:

   if ( Class::Error->errnum == 230 ) { .... }  # static
   if ( $obj->errnum == 230 ) { .... }

SUPPORT and FEEDBACK
If you need support or if you want just to send me some feedback or request, please use this link: http://perl.4pro.net/?Class::Error.

AUTHOR and COPYRIGHT
Copyright 2004-2005 by Domizio Demichelis.

All Rights Reserved. This module is free software. It may be used, redistributed and/or modified under the same terms as perl itself.