Hi Liz,
What I need is to preprocess the value before assigning it to an attribute.
I would do that in Perl5/Moose, using "around", like this:
package A;
use Moose;
has 'attribute' => (is => 'rw', isa => 'Str');
around [qw(attribute)] => sub {
my ($next, $self, $val) = @_;
return $self->$next unless $val;
return $self->$next(preprocess $val); # Preprocess the value before the
assignment
}
In this way I don't have to make an explicit call to the preprocessor any
time I assign a value to that attribute, effectively removing that from the
main program.
I'm looking for a way to do that in Perl6.
On Tue, Nov 14, 2017 at 6:11 PM, Elizabeth Mattijsen <[email protected]> wrote:
> > On 14 Nov 2017, at 18:06, Fernando Santagata <[email protected]>
> wrote:
> > I'm converting a program from Perl5/Moose.
> > I have several classes, each has some attributes that need to be
> processed in the same way before being passed to other objects.
> >
> > When I was using Moose, I had some "around" methods that would
> automatically modify the value before delivering it to those attributes, so
> delegating the object to do the needed adjustments.
> >
> > Stripped to the bare bones, the thing that in Perl6 looks like this:
> >
> > class A {
> > has $!a;
> >
> > method a($val?)
> > {
> > if $val.defined {
> > # Modify $val in some way
> > $!a = $val;
> > } else {
> > $!a;
> > }
> > }
> > }
> >
> > my A $a .= new;
> > # $a.a = 42; # This outputs an error
> > $a.a(42);
> > say $a.a;
> >
> > Any hint how to make it work as an assignment, instead of a method call?
> > Better yet, is there a way to abstract that behavior in a role?
>
> I think you want “is rw” on a public attribute?
>
> class A {
> has $.a is rw;
> }
> my $obj = A.new;
> $obj.a = 42;
> dd $obj;
> ===========
> A $obj = A.new(a => 42)
>
>
>
> Liz
--
Fernando Santagata
