Re^2: Moose and BUILD

[ikegami]

The type is specified using isa, and you need lazy => 1 to make sure the default isn't calculated too soon.

use Moose;

has 'x' => (
    is  => 'rw'
    isa => 'Num',
);

has 'y' => (
    is      => 'rw',
    isa     => 'Num',
    lazy    => 1,
    default => sub { sqrt($_[0])->x) },
);

[tj_thompson]

Good catch on the is, just a brain typo from rapidly throwing together running example code. It didn't matter in this case as I wasn't trying to use bad values in my test script.

I will look into the lazy flag on the attribute and get a better idea of what it does.

[ikegami]

Always use lazy when the initialiser relies on another field of $self.

It cause the initialiser to be called when the field is read instead of being called on construction.