(Moose/Hash): Can't call method "kv" on unblessed reference

locked_user sundialsvc4 has asked for the wisdom of the Perl Monks concerning the following question:

Trying to follow the example in Moose::Meta::Attribute::Native::Trait::Hash, specifically the example at the middle of the page under kv, with this code: (Perl 5.10.0 on OS/X)

package foo;
use Moose; 
has "k"=>(
  traits=>["Hash"],
  is=>"rw",
  isa=>"HashRef[Str]",
  default=>sub{{}}
);
my $f=foo->new();
print $f->k->kv;
[download]

... gives ...

Can't call method "kv" on unblessed reference

Incidentally, I find that ref($f) eq 'foo' and that ref($f->k) eq 'HASH'. So it is, indeed, “an unblessed reference.”

So, I guess I just really don't understand how these Trait thingies are supposed to work ... (A quick cover-your-asterisk check confirms that including or omitting handles as per the Synopsis makes no difference, as expected.)

I honestly think that I am writing the test exactly a shown in the page and it’s not working. I pray for Enlightenment.

Update: I now took the exact text of the example on the page and got the same result:

  package Stuff;
  use Moose;

  has 'options' => (
      traits    => ['Hash'],
      is        => 'ro',
      isa       => 'HashRef[Str]',
      default   => sub { {} },
      handles   => {
          set_option     => 'set',
          get_option     => 'get',
          has_no_options => 'is_empty',
          num_options    => 'count',
          delete_option  => 'delete',
          option_pairs   => 'kv',
      },
  );
my $object=Stuff->new(); 
for my $pair ( $object->options->kv ) {
      print "$pair->[0] = $pair->[1]\n";
  }
[download]

Replies are listed 'Best First'.
Re: (Moose/Hash): Can't call method "kv" on unblessed reference by chromatic (Archbishop) on Nov 16, 2011 at 23:45 UTC
The example in the documentation should probably read: `for my $pair ( $object->option_pairs ) { print "$pair->[0] = $pair->[1]\n"; }` [download] Is that clearer? Improve your skills with Modern Perl: the free book.	[reply] [d/l]
Re: (Moose/Hash): Can't call method "kv" on unblessed reference by ikegami (Patriarch) on Nov 17, 2011 at 00:18 UTC
You're trying to call `kv` on the hash ref returned by `$object->k`. Not gonna happen. Unblessed hash refs don't have methods. You mean to call a method you created for `$object` that's not even named `kv`. `$object->option_pairs` [download] PS — All your links are broken.	[reply] [d/l] [select]
Re^2: (Moose/Hash): Can't call method "kv" on unblessed reference by locked_user sundialsvc4 (Abbot) on Nov 17, 2011 at 01:08 UTC
Links removed. Thanks.
Re: (Moose/Hash): Can't call method "kv" on unblessed reference by locked_user sundialsvc4 (Abbot) on Nov 17, 2011 at 00:12 UTC
Okay, I figured it out by carefully examining the source-code of the `native_traits/trait_hash.t` test of this module. The example should read: (with the ~~strikeout~~ omitted ...) `for my $pair ( $object->options->kv ) {` Or, more appropriately to a real-world situation (as you did suggest): `for my $pair ( $object->options->option_pairs ) {` The accessor makes it possible to iterate through the values of, say, the `options` property of the object, by repeated calls to this method of the object ... it is not a method of the property itself. (AFAIK, Moose has no such concept.) The use of `handles` is, of course, the Right Goodness™ because, if (as you well might) you have more than one such property, you’ll need to define distinct accessor-names corresponding to each one and for that you of course must use `handles`. (That’s of course what it is for.)
Re: (Moose/Hash): Can't call method "kv" on unblessed reference by locked_user sundialsvc4 (Abbot) on Nov 16, 2011 at 23:50 UTC
Unfortunately... no dice. Using the copied example-code, as shown above with the change you suggested: `Can't call method "option_pairs" on unblessed reference at foo.pl line 19.` I’m afraid that this does not look to be “just an obvious tpyo.” Something about this doesn’t work, and I sincerely don’t know why. The perldoc makes no mention of, say, Perl-version dependencies, and I see no bug-reports that seem to be relevant. For completeness, the code being discussed now reads: `package Stuff; use Moose; has 'options' => ( traits => ['Hash'], is => 'ro', isa => 'HashRef[Str]', default => sub { {} }, handles => { set_option => 'set', get_option => 'get', has_no_options => 'is_empty', num_options => 'count', delete_option => 'delete', option_pairs => 'kv', }, ); my $object=Stuff->new(); for my $pair ( $object->options->option_pairs ) { print "$pair->[0] = $pair->[1]\n"; }` [download]