This might it then:
class A {
has $!a; # $.a if you want to be able to assign with .new
method a() {
Proxy.new(
FETCH => { $!a },
STORE => -> $, $value { $!a = $value * 2 }
)
}
}
my $a = A.new;
$a.a = 77;
dd $a.a; # 154
> On 14 Nov 2017, at 18:51, Fernando Santagata <[email protected]>
> wrote:
>
> Hi Liz,
>
> What I need is to preprocess the value before assigning it to an attribute.
>
> I would do that in Perl5/Moose, using "around", like this:
>
> package A;
> use Moose;
>
> has 'attribute' => (is => 'rw', isa => 'Str');
>
> around [qw(attribute)] => sub {
> my ($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
