我有两个对象属性需要昂贵的计算,所以我希望他们懒惰.它们最有效地计算在一起,所以我想同时计算它们.麋鹿是否提供了一种方法？
我想要的是“默认”或“构建器”,而不是返回默认值,它直接设置属性.返回值将被忽略.
has max_things =>
is => 'rw',isa => 'Int',lazy => 1,xxxxx => '_set_maxes';
has max_pairs =>
is => 'rw',xxxxx => '_set_maxes';
# Let's just assume this is an expensive calculation or the max_*
# attributes are used rarely and a lot of objects are created.
sub _set_maxes {
my $self = shift;
if( $self->is_32_bit ) {
$self->max_things(2**31);
$self->max_pairs(12345 * 2);
}
else {
$self->max_thing(2**63);
$self->max_pairs(23456 * 2);
}
return;
}
注意：我可以写我自己的“读者”或使用“周围”,但我宁愿保持声明,让Moose做这个工作.我也可以创建一个新对象来存储配对的值,但是对于两个值似乎是过度的.
解决方法
我不会说这是特别优雅,但它的作品…
use v5.14;
use warnings;
package Goose {
use Moose;
has max_things => (
is => 'rw',default => sub { shift->_build_maxes->max_things },);
has max_pairs => (
is => 'rw',default => sub { shift->_build_maxes->max_pairs },);
sub is_32_bit { 1 }
sub _build_maxes {
my $self = shift;
warn "Running builder...";
if( $self->is_32_bit ) {
$self->max_things(2**31);
$self->max_pairs(12345 * 2);
}
else {
$self->max_thing(2**63);
$self->max_pairs(23456 * 2);
}
$self; # helps chaining in the defaults above
}
}
my $goose = Goose->new;
say $goose->max_things;
say $goose->max_pairs;