perl - 如何在 Perl 对象中定义前/后增量行为？

Question

Date::Simple 对象显示此行为，其中 $date++返回第二天的日期。

Date::Simple objects are immutable. After assigning $date1 to $date2, no change to $date1 can affect $date2. This means, for example, that there is nothing like a set_year operation, and $date++ assigns a new object to $date.

如何自定义对象的前/后增量行为，例如 ++$object或 $object--执行特定操作？

我浏览过 perlboot , perltoot , perltooc和 perlbot ，但我没有看到任何示例说明如何做到这一点。

Answer 1

您要 overload .

package Number;

use overload
    '0+'    => \&as_number,
    '++'    => \&incr,
;

sub new {
    my ($class, $num) = @_;

    return bless \$num => $class;
}

sub as_number {
    my ($self) = @_;

    return $$self;
}

sub incr {
    my ($self) = @_;

    $_[0] = Number->new($self->as_number + 1); # note the modification of $_[0]
    return;
}

package main;

my $num = Number->new(5);
print $num      . "\n"; # 5
print $num++    . "\n"; # 5
print ++$num    . "\n"; # 7