Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

I have a few attributes in my class which are instances of other (heavy) classes. I don't want to incur a startup overhead of loading all these heavy classes unless the user accesses the attributes. To illustrate:

package MyClass;
use Any::Moose;
use Foo::Heavy; # slows startup!
has foo => (is => 'ro', default => sub { Foo::Heavy->new });

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I want the 'foo' attribute to behave something like this: 
sub foo {
    my ($self) = @_;
    state $foo;
    if (!$foo) {
        require Foo::Heavy;
        $foo = Foo::Heavy->new;
    }
    $foo;
}

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Is there an easy way to do this in Moose?

Replies are listed 'Best First'.
Re: Moose/Mouse: assigning default to attribute on first access?
by bobr (Monk) on Jan 11, 2011 at 12:38 UTC
    You can set lazy on foo atribute and require in default. It will be called after foo is accessed. 
    package MyClass;
use Any::Moose;

has foo => (
    is      => 'ro',
    lazy    => 1,
    default => sub {
        require Foo::Heavy;
        Foo::Heavy->new;
    },
);

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    -- regards, Roman

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[d/l]
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Re: Moose/Mouse: assigning default to attribute on first access?
by Anonymous Monk on Jan 11, 2011 at 12:31 UTC
    Set your attribute to lazy => 1. This is very useful when some attributes' builder functions rely on others' values.
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[d/l]
      Perfect, I knew Moose is awesome like that.
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