Re^2: Moose and BUILD

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) },
);
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Re^3: Moose and BUILD by tj_thompson (Monk) on Jun 15, 2011 at 21:04 UTC
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.	[reply]
Re^4: Moose and BUILD by ikegami (Patriarch) on Jun 15, 2011 at 21:19 UTC
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.	[reply] [d/l]