NAME

Class::Error - Delayed checking of object failure

VERSION 2.40

Included in OOTools 2.21 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

POD ERRORS

Hey! The above document had some coding errors, which are explained below: