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

In reply to Re: Moose/Mouse: assigning default to attribute on first access? by bobr
in thread Moose/Mouse: assigning default to attribute on first access? by Anonymous Monk

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