Perl Moose 对象可以直接具有数组/哈希属性吗？

Question

Can be done something like this in Perl?

package Person;
use Moose;

has 'friends' => ( is => 'rw', isa => 'Array', default => () );

I see that perl compiler doesn't accept this particular syntax, but do I use wrong syntax, or it is not possible at all? Do I have to use an array reference instead?

I'm pretty new to perl so the question is maybe dumb and I somehow feel the answer would be "no", but I haven't found any mention about it.

Thanks in advance

Answer 1

"List" has quite a few definitions. Presuming you mean an collection or ordered collection of Person objects, I'd use an array I'd pass to the accessor using a reference

has friends => (
   is      => 'rw',
   isa     => 'ArrayRef[Person]',
   default => sub { [] },
);

push @{ $o->friends }, $person;

for (@{ $o->friends }) {
   ...
}

You can add useful methods using Moose::Meta::Attribute::Native::Trait::Array .

has friends => (
   traits  => [qw( Array )],
   is      => 'rw',
   isa     => 'ArrayRef[Person]',
   default => sub { [] },
   handles => {
      push_friends => 'push',
   },
);

$o->push_friends($person);

for (@{ $o->friends }) {
   ...
}

Answer 2

It's not quite what you're asking, but look at array traits - http://search.cpan.org/dist/Moose/lib/Moose/Meta/Attribute/Native/Trait/Array.pm . Since all of an instance's values are stored in a hashref, you can not store anything other than scalar values, meaning you need to use references. This handles all of the boilerplate you need to work with the internal arrayref.

package Person;
use Moose;

has 'friends' => ( is => 'ro', 
                   traits  => ['Array'],
                   isa => 'ArrayRef[Str]',
                   default => sub { [] },
                   handles => {
                                 all_friends    => 'elements',
                                 add_friend     => 'push',
                                 map_friends    => 'map',
                                 filter_friends => 'grep',
                                 find_friend    => 'first',
                                 get_friend     => 'get',
                                 join_friends   => 'join',
                                 count_friends  => 'count',
                                 has_friends    => 'count',
                                 has_no_friends => 'is_empty',
                                 sorted_friends => 'sort',
                             },

                 );

Answer 3

As a simple answer that at least makes the get/set easier, you can write your own accessor functions to wrap an array ref into an array. For example:

package Person;
use Moo;

has 'friendsRef' => ( is => 'rw', default => sub { []; } );

## A 'set/get' wrapper for friendsRef
sub Person::friends {
  my ($self, @list) = @_;
  return @{$self->friendsRef} unless $#list>=0;
  return $self->friendsRef(\@list);
}

## Example bonus function for adding to list
sub Person::addFriends {
  my ($self, @list) = @_;
  return push(@{$self->friendsRef}, @list);
}

Example code usage could be:

my $p = Person->new();

$p->friends('Dave','Jerry');
print "Friends are: ",join(', ',$p->friends()),"\n";

$p->friends('Bob','Dave');
print "Friends are: ",join(', ',$p->friends()),"\n";

$p->addFriends('Joe','Cletus');
print "Friends are: ",join(', ',$p->friends()),"\n";

## Note that "$p->friends()" is not a scalar, it's a sub returning an array,
## so instead of "$#{$p->friends()}" you'd want "scalar($p->friends())"
print "Number of friends is ",scalar($p->friends()),"\n";

Output is:

Friends are: Dave, Jerry          
Friends are: Bob, Dave            
Friends are: Bob, Dave, Joe, Cletus                                 
Number of friends is 4