Ewan Birney

NAME

Bio::Root::Err.pm - Exception class for Perl 5 objects

SYNOPSIS

Object Creation

Bio::Root::Object.pm is a wrapper for Bio::Root::Err.pm objects so clients do not have to create these objects directly. Please see Bio::Root::Object::throw() as well as _initialize() for a more complete treatment of how to create Bio::Root::Err.pm objects.

  use Bio::Root::Err;

  $err = Bio::Root::Err->new(-MSG     =>"Bad data: $data",
                             -STACK   =>[\caller(0), \caller(1), ...],
                             );

To use the throw() method directly:

  use Bio::Root::Err (:std);

  throw( $object_ref, 'Error message', 'additional note', 'technical note');

The $object_ref argument should be a reference to a Bio::Root::Object.pm.

See also the USAGE section .

INSTALLATION

This module is included with the central Bioperl distribution:

   http://bio.perl.org/Core/Latest
   ftp://bio.perl.org/pub/DIST

Follow the installation instructions included in the README file.

DESCRIPTION

A Bio::Root::Err.pm object encapsulates data and methods that facilitate working with errors and exceptional conditions that arise in Perl objects. There are no biological semantics in this module, as one may suspect from its location in the Bio:: hierarchy. The location of this module serves to separate it from the namespaces of other Perl Error modules. It also makes it convenient for use by Bio:: objects.

The motivation for having an error object is to allow Perl 5 objects to deal with errors or exceptional conditions that can arise during their construction or manipulation. For example:

 (1) A complex object can break in many ways.
 (2) Tracking errors within a set of nested objects can be difficult.
 (3) The way an error is reported should be context-sensitive:
     a web-user needs different information than does the
     software engineer.

Bio::Root::Err.pm, along with Bio::Root::Object.pm, attempt to make such problems tractable. Please see the Bio::Root::Object.pm documentation for more about my error handling philosophy.

A Bio::Root::Err.pm object is an example of a Vector-Object: This module inherits both from Bio::Root::Object.pm and Bio::Root::Vector.pm. This permits a single Err object to exist within a linked list of Err objects OR alone. See the Bio::Root::Vector.pm documentation for more about Vector-Objects.

The API for this module is not complete since the module is under development.

Other Exception Strategies

Exception handling with Perl 5 objects is currently not as evolved as one would like. The error handling used by Bio::Root::Object.pm and Bio::Root::Err.pm relies on Perl's built-in error/exception handling with eval/die, which is not very object-aware. What I've attempted to do with these modules is to make eval/die more object-savvy, as well as make Perl 5 objects more eval/die-savvy (but the current strategy is basically a hack).

It would be great if Perl could throw an object reference with die(). This would permit more intelligent and easy to write exception handlers. For now the Err.pm object is reconstructed from the output of string().

There are some other third-party Exception classes such as Torsten Ekedahl's Experimental::Exception.pm or Ken Steven's Throwable.pm or Graham Barr's Error.pm (see "Other Exception Modules"). These modules attempt to introduce a traditional "try-catch-throw" exception handling mechanism into Perl. Future version of my modules (and perhaps erl itself) may utilize one of these.

USAGE

A demo script that illustrates working with Bio::Root::Err objects is available at:

    http://bio.perl.org/Core/Examples/Root_object/error.pl

DEPENDENCIES

Bio::Root::Err.pm inherits from Bio::Root::Object.pm and Bio::Root::Vector.pm.

FEEDBACK

Mailing Lists

User feedback is an integral part of the evolution of this and other Bioperl modules. Send your comments and suggestions preferably to one of the Bioperl mailing lists. Your participation is much appreciated.

  bioperl-l@bioperl.org             - General discussion
  http://bioperl.org/MailList.shtml - About the mailing lists

Reporting Bugs

Report bugs to the Bioperl bug tracking system to help us keep track the bugs and their resolution. Bug reports can be submitted via email or the web:

    bioperl-bugs@bio.perl.org
    http://bio.perl.org/bioperl-bugs/

AUTHOR Steve Chervitz

Email sac@bioperl.org

See the FEEDBACK section section for where to send bug reports and comments.

VERSION

Bio::Root::Err.pm, 0.041

SEE ALSO

  Bio::Root::Object.pm    - Core object
  Bio::Root::Vector.pm    - Vector object
  Bio::Root::Global.pm    - Manages global variables/constants

  http://bio.perl.org/Projects/modules.html  - Online module documentation
  http://bio.perl.org/                       - Bioperl Project Homepage

Other Exception Modules

  Experimental::Exception.pm   - ftp://ftp.matematik.su.se/pub/teke/
  Error.pm                     - http://www.cpan.org/authors/id/GBARR/
  Throwable.pm                 - mailto:kstevens@globeandmail.ca

  http://genome-www.stanford.edu/perlOOP/exceptions.html

ACKNOWLEDGEMENTS

This module was developed under the auspices of the Saccharomyces Genome Database: http://genome-www.stanford.edu/Saccharomyces

Other Bioperl developers contributed ideas including Ewan Birney, Ian Korf, Chris Dagdigian, Georg Fuellen, and Steven Brenner.

COPYRIGHT

Copyright (c) 1996-8 Steve Chervitz. All Rights Reserved. This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

TODO

  • Improve documentation.

  • Experiment with other Exception modules.

APPENDIX

Methods beginning with a leading underscore are considered private and are intended for internal use by this module. They are not considered part of the public interface and are described here for documentation purposes only.

_initialize

 Usage     : n/a; automatically called by Bio::Root::Object::new()
 Purpose   : Initializes key Bio::Root::Err.pm data.
 Returns   : String (the -MAKE constructor option.)
 Argument  : Named parameters passed from new()
           : (PARAMETER TAGS CAN BE UPPER OR LOWER CASE).
           :   -MSG     => basic description of the exception.
           :   -NOTE    => additional note to indicate cause of exception
           :               or provide information about how to fix/report it
           :   -TECH    => addition note with technical information
           :               of interest to developer.
           :   -STACK   => array reference containing caller() data
           :   -TYPE    => string, one of @Bio::Root::Err::ERR_TYPES
           :               (default = exception).
           :   -CONTEXT => array reference
           :   -OBJ     => Err object to be cloned.

See Also : Bio::Root::Object::_set_err()

_set_clone

 Usage     : n/a; internal method used by _initialize()
 Purpose   : Copy all Bio::Root::Err.pm data members into a new object reference.
 Argument  : object ref for object to be cloned.
 Comments  : Does not cloning the vector since this method is
           : typically used to extract a single Err object from its vector.

_build_from_string

 Usage     : n/a; called by _initialize()
 Purpose   : Re-create an Err.pm object from a string containing Err data.
 Returns   : boolean, (was the Err.pm object rebuilt?)
 Argument  : message, note, tech passed from _initialize()
           : The message is examined to see if it contains a stringified error.

See Also : _initialize(), string(), _has_err()

_has_err

 Usage     : n/a; internal method called by _build_from_string()
 Purpose   : Deterimine if an Err has already been set to prevent duplicate Errs.
 Returns   : boolean

See Also : _build_from_string()

_set_type

 Usage     : n/a; internal method
 Purpose   : Sets the type of Err (warning, exception, fatal)
           : Called by _initialize()
 Argument  : string

_set_list_data

 Usage     : n/a; internal method used by set().
           : $err->_set_list_data( $member, $data);
 Purpose   : For data members which are anonymous arrays: note, tech, stack,
           : adds the given data to the list.
 Arguments : $member = any of qw(note tech stack)
           : $data   = string
 Comments  : Splits $data on tab. Each item
           : of the split is a new entry.
           : To clobber the current data (unusual situation), you must first
           : call set() with no data then call again with desired data.

_set_context

 Usage     : n/a; internal method used by set().
 Purpose   : Sets the object containment context for the exception.
           : (this is the hierarchy of objects in which the
           :  exception occurred.)

set

 Usage     : $err->set( $member, $data );
 Purpose   : General accessor for setting any Err.pm data member.
 Example   : $err->set('note', 'this is an additional note.');
 Returns   : n/a
 Argument  : $member = string, any of qw(msg type note tech stack)
           : $data   = string
 Throws    : n/a
 Comments  : Note, tech, and stack items are appended to any existing
           : notes, tech notes, and stack.
           : There should be no need to mess with the stack.

msg

 Usage     : $message = $err->msg;
 Purpose   : Get the main message associated with the exception.
 Returns   : String
 Argument  : optional string to be used as a delimiter.

See Also : get(), string()

type

 Usage     : $type = $err->type;
 Purpose   : Get the type of Err (warning, exception, fatal)
 Returns   : String
 Argument  : optional string to be used as a delimiter.

See Also : get(), string()

note

 Usage     : $note = $err->note;
           : $note = $err->note('<P>');
 Purpose   : Get any general note associated with the exception.
 Returns   : String
 Argument  : optional string to be used as a delimiter.

See Also : get(), string()

tech

 Usage     : $tech = $err->tech;
           : $tech = $err->tech('<P>');
 Purpose   : Get any technical note associate with the exception.
 Returns   : String
 Argument  : optional string to be used as a delimiter.

See Also : get(), string()

stack

 Usage     : $stack = $err->stack;
           : $stack = $err->stack('<P>');
 Purpose   : Get the call stack for the exception.
 Returns   : String
 Argument  : optional string to be used as a delimiter.

See Also : get(), string()

context

 Usage     : $context = $err->context;
           : $context = $err->context('<P>');
 Purpose   : Get the containment context of the object which generated the exception.
 Returns   : String
 Argument  : optional string to be used as a delimiter.

See Also : get(), string()

get

 Usage     : $err->get($member, $delimiter);
 Purpose   : Get specific data from the Err.pm object.
 Returns   : String in scalar context.
           : Array in list context.
 Argument  : $member = any of qw(msg type note tech stack context) or combination.
           : $delimiter = optional string to be used as a delimiter
           : between member data.

See Also : string(), msg(), note(), tech(), type(), context(), stack()

_get_list_data

 Usage     : n/a; internal method used by get()
 Purpose   : Gets data for members which are list refs (note, tech, stack, context)
 Returns   : Array
 Argument  : ($member, $delimiter)

See Also : get()

get_all

 Usage     : (same as get())
 Purpose   : Get specific data from all errors in an Err.pm object.
 Returns   : Array in list context.
           : String in scalar context.
 Argument  : (same as get())

See Also : get()

_add_note

 Usage     : n/a; internal method called by _add_list_data()
 Purpose   : adds a new note.

See Also : _add_list_data()

_add_tech()

 Usage     : n/a; internal method called by _add_list_data()
 Purpose   : adds a new technical note.

See Also : _add_list_data()

_add_list_data

 Usage     : n/a; called by _set_list_data()
 Purpose   : adds a new note or tech note.

See Also : _set_list_data()

print

 Usage     : $err->print;
 Purpose   : Prints Err data to STDOUT or a FileHandle.
 Returns   : Call to print
 Argument  : Named parameters for string()
 Comments  : Uses string() to get data.

See Also : string()

string

 Usage     : $err->string( %named_parameters);
 Purpose   : Stringify the data contained in the Err.pm object.
 Example   : print STDERR $err->string;
 Returns   : String
 Argument  : Named parameters (optional) passed to
           : Bio::Root::IOManager::set_display().

See Also : print(), _build_from_string(), Bio::Root::IOManager::set_display()

is_fatal

 Usage     : $err->is_fatal;
 Purpose   : Determine if the error is of type 'FATAL'
 Returns   : Boolean
 Status    : Experimental, Deprecated

throw

 Usage     : throw($object, [message], [note], [technical note]);
           : This method is exported.
 Purpose   : Class method version of Bio::Root::Object::throw().
 Returns   : die()s with the contents of the Err object in a string.
           : If the global strictness is less than -1, die is not called and
           : the error is printed to STDERR.
 Argument  : [0] = object throwing the error.
           : [1] = optional message about the error.
           : [2] = optional note about the error.
           : [3] = optional technical note about the error.
 Comments  : The glogal verbosity level is not used. For verbosity-sensitive
           : behavior, use Bio::Root::Object::throw().
 Status    : Experimental
           : This method is an alternative to Bio::Root::Object::throw()
           : and is not as well developed or documented as that method.

See Also : warning(), Bio::Root::Object::throw() Bio::Root::Global::strictness()

warning

 Usage     : warning($object, [message], [note], [technical note]);
           : This method is exported.
 Purpose   : Class method version of Bio::Root::Object::warn().
 Returns   : Prints the contents of the error to STDERR and returns false (0).
           : If the global strictness() is > 1, warn() calls are converted
           : into throw() calls.
 Argument  : [0] = object producing the warning.
           : [1] = optional message about the error.
           : [2] = optional note about the error.
           : [3] = optional technical note about the error.
           :
 Comments  : The glogal verbosity level is not used. For verbosity-sensitive
           : behavior, use Bio::Root::Object::warn().
 Status    : Experimental
           : This method is an alternative to Bio::Root::Object::warn()
           : and is not as well developed or documented as that method.

See Also : throw, Bio::Root::Object::warn(), Bio::Root::Global::strictness()

format_stack_entry

 Usage     : &format_stack_entry(<class>,<file>,<line>,<class_method>,<has_args>,<wantarray>)
           : This function is exported.
 Purpose   : Creates a single stack entry given a caller() list.
 Argument  : List of scalars (output of the caller() method).
 Returns   : String = class_method($line)
           : e.g., Bio::Root::Object::name(1234)

FOR DEVELOPERS ONLY

Data Members

Information about the various data members of this module is provided for those wishing to modify or understand the code. Two things to bear in mind:

1 Do NOT rely on these in any code outside of this module.

All data members are prefixed with an underscore to signify that they are private. Always use accessor methods. If the accessor doesn't exist or is inadequate, create or modify an accessor (and let me know, too!).

2 This documentation may be incomplete and out of date.

It is easy for this documentation to become obsolete as this module is still evolving. Always double check this info and search for members not described here.

An instance of Bio::Root::Err.pm is a blessed reference to a hash containing all or some of the following fields:

 FIELD     VALUE
 ------------------------------------------------------------------------
 _type     fatal | warning | exception (one of @Bio::Root::Err::ERR_TYPES).

 _msg      Terse description: Main cause of error.

 _note     List reference. Verbose description: probable cause & troubleshooting for user.

 _tech     List reference. Technical notes of interest to programmer.

 _stack    List reference. Stack trace: list of "class::method(line number)" strings.