如何根据另一个属性将属性约束从触发器提升为类型细化？

问题描述

这有效：

use Moops;
class Foo :ro {
    use Types::Common::Numeric qw(PositiveOrZeroInt);
    has from => required => true,isa => PositiveOrZeroInt;
    has to => required => true,isa => PositiveOrZeroInt,trigger => method($to) {
        die 'must be from ≤ to' unless $self->from <= $to
    };
}
Foo->new(from => 0,to => 1); # ok
Foo->new(from => 1,to => 0); # "must be from ≤ to at …"

我希望能够以某种方式使约束成为该类型的一部分。

use Moops;
class Bar :ro {
    use Types::Common::Numeric qw(PositiveOrZeroInt);
    has from => required => true,isa => PositiveOrZeroInt->where(sub {
        $self->from <= $_
    });
}
Bar->new(from => 0,to => 1);
# Global symbol "$self" requires explicit package name
# (did you forget to declare "my $self"?)

我检查了where sub仅收到一个参数。

解决方法

如果要在类型检查中执行此操作，则可以将两个属性组合为一个属性，该属性将是一个包含两个数字的arrayref。

use Moops;

class Foo :ro {
    use Types::Standard qw(Tuple);
    use Types::Common::Numeric qw(PositiveOrZeroInt);
    
    has from_and_to => (
        required => true,isa      => Tuple->of(PositiveOrZeroInt,PositiveOrZeroInt)->where(sub {
            $_->[0] <= $_->[1];
        }),# Provide `from` and `to` methods to fetch values
        handles_via => 'Array',handles => {
            'from' => [ get => 0 ],'to'   => [ get => 1 ],},);
    
    # Allow `from` and `to` to be separate in the constructor
    method BUILDARGS {
        my %args = ( @_==1 ? %{$_[0]} : @_ );
        $args{from_and_to} ||= [ $args{from},$args{to} ];
        \%args;
    }
}

Foo->new(from => 0,to => 1); # ok
Foo->new(from => 1,to => 0); # "must be from ≤ to at …"

我不会在类型检查中这样做。如果属性是只读的，那么我将在BUILD中进行操作（否，不是BUILDARGS），如果属性是可读写的，我将在trigger中进行操作。