Class::ReturnValue - A return-value object that lets you treat it

Class-ReturnValue documentation Contained in the Class-ReturnValue distribution.

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NAME

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Class::ReturnValue - A return-value object that lets you treat it as as a boolean, array or object

DESCRIPTION

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Class::ReturnValue is a "clever" return value object that can allow code calling your routine to expect: a boolean value (did it fail) or a list (what are the return values)

EXAMPLE

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    sub demo {
        my $value = shift;
        my $ret = Class::ReturnValue->new();
        $ret->as_array('0', 'No results found');

        unless($value) {
            $ret->as_error(errno => '1',
                               message => "You didn't supply a parameter.",
                               do_backtrace => 1);
        }

        return($ret->return_value);
    }

    if (demo('foo')){ 
        print "the routine succeeded with one parameter";
    }
    if (demo()) {
        print "The routine succeeded with 0 paramters. shouldn't happen";
    } else {
        print "The routine failed with 0 parameters (as it should).";
    }




    my $return = demo();
    if ($return) {
        print "The routine succeeded with 0 paramters. shouldn't happen";
    } else {
        print "The routine failed with 0 parameters (as it should). ".
              "Stack trace:\n".
        $return->backtrace;
    }

    my @return3 = demo('foo');
    print "The routine got ".join(',',@return3).
          "when asking for demo's results as an array";




    my $return2 = demo('foo');

    unless ($return2) {
        print "The routine failed with a parameter. shouldn't happen.".
             "Stack trace:\n".
        $return2->backtrace;
    }

    my @return2_array = @{$return2}; # TODO: does this work
    my @return2_array2 = $return2->as_array;

METHODS

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Instantiate a new Class::ReturnValue object

Return the 'as_array' attribute of this object as an array.

If $self is called in an array context, returns the array specified in ARRAY

Turns this return-value object into an error return object. TAkes three parameters:

    message
    do_backtrace
    errno 

    'message' is a human readable error message explaining what's going on

    'do_backtrace' is a boolean. If it's true, a carp-style backtrace will be 
    stored in $self->{'backtrace'}. It defaults to true

    errno and message default to undef. errno _must_ be specified. 
    It's a numeric error number.  Any true integer value  will cause the 
    object to evaluate to false in a scalar context. At first, this may look a 
    bit counterintuitive, but it means that you can have error codes and still 
    allow simple use of your functions in a style like this:




        if ($obj->do_something) {
            print "Yay! it worked";
        } else {
            print "Sorry. there's been an error.";
        }




        as well as more complex use like this:

        my $retval = $obj->do_something;

        if ($retval) {
            print "Yay. we did something\n";
            my ($foo, $bar, $baz) = @{$retval};
            my $human_readable_return = $retval;
        } else {
            if ($retval->errno == 20) {
                die "Failed with error 20 (Not enough monkeys).";
            } else {
                die  $retval->backtrace; # Die and print out a backtrace 
            }
        }

Returns the errno if there's been an error. Otherwise, return undef

If there's been an error return the error message.

If there's been an error and we asked for a backtrace, return the backtrace. Otherwise, return undef.

If there's been an error, return undef. Otherwise return 1

AUTHOR

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    Jesse Vincent <jesse@bestpractical.com>

BUGS

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    This module has, as yet, not been used in production code. I thing
    it should work, but have never benchmarked it. I have not yet used
    it extensively, though I do plan to in the not-too-distant future.
    If you have questions or comments,  please write me.

    If you need to report a bug, please send mail to 
    <bug-class-returnvalue@rt.cpan.org> or report your error on the web
    at http://rt.cpan.org/

COPYRIGHT

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    Copyright (c) 2002,2003,2005,2007 Jesse Vincent <jesse@bestpractical.com>
    You may use, modify, fold, spindle or mutilate this module under
    the same terms as perl itself.

SEE ALSO

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    Class::ReturnValue isn't an exception handler. If it doesn't
    do what you want, you might want look at one of the exception handlers
    below:

    Error, Exception, Exceptions, Exceptions::Class

    You might also want to look at Contextual::Return, another implementation
    of the same concept as this module.
Class-ReturnValue documentation Contained in the Class-ReturnValue distribution. 
use warnings;
use strict;

package Class::ReturnValue;




use Exporter;

use vars qw/$VERSION @EXPORT @ISA/;

@ISA = qw/Exporter/;
@EXPORT = qw /&return_value/;
use Carp;
use Devel::StackTrace;
use Data::Dumper;


$VERSION = '0.55';


use overload 'bool' => \&error_condition;
use overload '""' => \&error_condition;
use overload 'eq' => \&my_eq;
use overload '@{}' => \&as_array;
use overload 'fallback' => \&as_array;



sub new {
    my $self = {};
    bless($self);
    return($self);
}

sub my_eq {
    my $self = shift;
    if (wantarray()) {
        return($self->as_array);
    }
    else {
        return($self);
    }    
}


sub as_array {

    my $self = shift;
    if (@_) { 
        @{$self->{'as_array'}} = (@_);
    }
    return(@{$self->{'as_array'}});
}



sub as_error {
    my $self = shift;
    my %args = ( errno => undef,
                 message => undef,
                 do_backtrace => 1,
                 @_);

    unless($args{'errno'}) {
        carp "$self -> as_error called without an 'errno' parameter";
        return (undef);
    }

    $self->{'errno'} = $args{'errno'};
    $self->{'error_message'} = $args{'message'};
    if ($args{'do_backtrace'}) {
        # Use carp's internal backtrace methods, rather than duplicating them ourselves
         my $trace = Devel::StackTrace->new(ignore_package => 'Class::ReturnValue');

        $self->{'backtrace'} = $trace->as_string; # like carp
    }

    return(1);
}



sub errno { 
    my $self = shift;
    if ($self->{'errno'}) {
        return ($self->{'errno'});
     }
     else {
        return(undef);
     }
}



sub error_message {
    my $self = shift;
    if ($self->{'error_message'}) {
        return($self->{'error_message'});
    }
    else {
        return(undef);
    }
}



sub backtrace {
    my $self = shift;
    if ($self->{'backtrace'}) {
        return($self->{'backtrace'});
    }
    else {
        return(undef);
    }
}


sub error_condition { 
    my $self = shift;
    if ($self->{'errno'}) {
            return (undef);
        }
        elsif (wantarray()) {
            return(@{$self->{'as_array'}});
        }
       else { 
            return(1);
       }     
}

sub return_value {
    my $self = shift;
    if (wantarray) {
         return ($self->as_array);
    }
    else {
       return ($self);
    }
}



1;