Excerpts from Evan Carroll's message of Tue Nov 03 11:38:47 -0500 2009:
> On Tue, Nov 3, 2009 at 10:01 AM, Ovid <publiustemp-catal...@yahoo.com> wrote:
> > When parsing documents, if my code finds more than one title in a document,
> > it's an error because we don't know which title is needed. The user should
> > be able to override this in the constructor and provide their own title
> > (this is actually true for several attributes):
>
> So the mechanism you're looking for is (1) if the title is not set in
> the constructor and (2) if it has already been set in runtime then (3)
> die. This can be accomplished easy enough, with around and a
> predicate, and it will ensure consistency throughout the program and
> anything that subclasses it.
>
> has 'attribute' => ( isa => 'Str', is => 'ro', predicate => 'has_attribute' );
>
> around 'attribute' => sub {
> my ($next, $this, $key) = @_;
> $self->has_attribute ? die 'exception' : $this->$next($key);
> };
You need 'rw', not 'ro'. Also, you forgot to handle setting and getting
separately.
This might be preferable to my suggestion if your object's methods are being
called mid-parse, rather than building up a data structure first and setting
attributes based on it after parsing is done. Even then, I think I'd rather
have a separate method than modify the accessor.
hdp.
