Attribute-Handlers

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README  view on Meta::CPAN

    Note that, because the "Cycle" attribute receives its arguments in the
    $data variable, if the attribute is given a list of arguments, $data
    will consist of a single array reference; otherwise, it will consist of
    the single argument directly. Since Tie::Cycle requires its cycling
    values to be passed as an array reference, this means that we need to
    wrap non-array-reference arguments in an array constructor:

        $data = [ $data ] unless ref $data eq 'ARRAY';

    Typically, however, things are the other way around: the tieable class
    expects its arguments as a flattened list, so the attribute looks like:

        sub UNIVERSAL::Cycle : ATTR(SCALAR) {
            my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
            my @data = ref $data eq 'ARRAY' ? @$data : $data;
            tie $$referent, 'Tie::Whatever', @data;
        }

    This software pattern is so widely applicable that Attribute::Handlers
    provides a way to automate it: specifying 'autotie' in the "use
    Attribute::Handlers" statement. So, the cycling example, could also be

README  view on Meta::CPAN

        sub foo : Purpose(to foo all data before barring it) { }

        # etc.

UTILITY FUNCTIONS
    This module offers a single utility function, "findsym()".

    findsym
            my $symbol = Attribute::Handlers::findsym($package, $referent);

        The function looks in the symbol table of $package for the typeglob
        for $referent, which is a reference to a variable or subroutine
        (SCALAR, ARRAY, HASH, or CODE). If it finds the typeglob, it returns
        it. Otherwise, it returns undef. Note that "findsym" memoizes the
        typeglobs it has previously successfully found, so subsequent calls
        with the same arguments should be much faster.

DIAGNOSTICS
    "Bad attribute type: ATTR(%s)"
        An attribute handler was specified with an ":ATTR(*ref_type*)", but
        the type of referent it was defined to handle wasn't one of the five

lib/Attribute/Handlers.pm  view on Meta::CPAN

Note that, because the C<Cycle> attribute receives its arguments in the
C<$data> variable, if the attribute is given a list of arguments, C<$data>
will consist of a single array reference; otherwise, it will consist of the
single argument directly. Since Tie::Cycle requires its cycling values to
be passed as an array reference, this means that we need to wrap
non-array-reference arguments in an array constructor:

    $data = [ $data ] unless ref $data eq 'ARRAY';

Typically, however, things are the other way around: the tieable class expects
its arguments as a flattened list, so the attribute looks like:

    sub UNIVERSAL::Cycle : ATTR(SCALAR) {
	my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
	my @data = ref $data eq 'ARRAY' ? @$data : $data;
	tie $$referent, 'Tie::Whatever', @data;
    }


This software pattern is so widely applicable that Attribute::Handlers
provides a way to automate it: specifying C<'autotie'> in the

lib/Attribute/Handlers.pm  view on Meta::CPAN

=head1 UTILITY FUNCTIONS

This module offers a single utility function, C<findsym()>.

=over 4

=item findsym

    my $symbol = Attribute::Handlers::findsym($package, $referent);

The function looks in the symbol table of C<$package> for the typeglob for
C<$referent>, which is a reference to a variable or subroutine (SCALAR, ARRAY,
HASH, or CODE). If it finds the typeglob, it returns it. Otherwise, it returns
undef. Note that C<findsym> memoizes the typeglobs it has previously
successfully found, so subsequent calls with the same arguments should be
much faster.

=back

=head1 DIAGNOSTICS