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Data::Annotation::Rule


=head1 SYNOPSIS

   use Data::Annotation::Rule;


=head1 DESCRIPTION

Representation of a rule, meant to be used by L<Data::Annotation>.

=head1 INTERFACE

=head2 Constructor

   my $rule = Data::Annotation::Rule->(%opts);

Make a new instance for a rule.

Input parameter C<condition> is supposed to be compatible with
L<Data::Annotation::Expression>, either by being an instance itself or
by being suitable to create a new instance.

=head2 Accessors

=head3 B<< condition >>

   my $condition = $rule->condition;

The condition that is checked to see if the rule applies or not. It must
be compatible with L<Data::Annotation::Expression> and will be used as a
boolean expression.

=head3 B<< description >>

   my $text = $rule->description;

An optional description for the rule definition. It will be useful for
you in a couple of months, after you forgot everything about it.

=head3 B<< name >>

   my $text = $rule->name;

An explicit name for the rule, useful for debugging (it is printed when
a rule matches and debug or trace is enabled).

=head3 B<< parse_context >>

   my $ctx = $rule->parse_context;

Whatever was passed as argument C<condition-parse-context>, which can
help set the stage for condition parsing. This should not be generally
needed, but still. See L<Data::Annotation::Expression> for more details.

=head3 B<< record >>

   my $defs = $rule->record;

A data structure to drive changes in the C<$overlay> passed to
L</evaluate> in case the condition applies. This allows recording some
data that can be later used by other chains/rules during following
evaluations.

Accepts a hash reference with the following keys:

=over

=item *

C<delete>: an array reference of I<paths> suitable for
L</Data::Annotation::Traverse::traverse_plain>, these paths will be
marked as deleted in the overlay.

=item *

C<set>: a hash reference of I<paths>/values to be set in the overlay.

=back

All paths are supposed to be relative to an initial key C<run>, which is
mapped onto the C<$overlay> in L</execute>.

As an example, let's consider the following chains definitions:

   # ...
   EHLO:
     default: reject
     rules:
       - condition:
           and:
             - eq: [ '.peer_ip', '=127.0.0.1' ]
             - eq: [ '.peer_identity', '=localhost.localdomain' ]
         record:
           set:
             '.caller': localhost
         return: accept

   DATA:
     default: reject
     rules:
       - name: localhost/size
         condition:
           and:
             - eq: [ '.caller', '=localhost' ]
             - '<': [ '.mail_min_size', '=250' ]
         return: accept
   # ...

When the C<EHLO> chain is called and the first (and only) rule is
matched, then a new parameter at position C<run.caller> is set to the
literal value C<localhost>. This can then be used at a later call to
rule C<DATA>, allowing to avoid repeating all the tests and adding
readability to the whole condition.

=head3 B<< retval >>

   my $retval = $rule->retval;

The result (annotation) value returned by L</evaluate> when the
condition of the rule applies.

Initialized by key C<return> in the constructor.


=head2 Methods

=head3 B<< evaluate >>

   my $result = $rule->evaluate($overlay);

Evaluate the annotation for data wrapped in some C<$overlay>.


=head1 ANYTHING ELSE (INCLUDING AUTHOR, COPYRIGHT AND LICENSE)

See documentation for Data::Annotation.


=cut