Assigning to a ArrayRef accessor type

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

Hi Monks,
I am struggling to understand how I can assign to an ArrayRef accessor. I am trying to use Moo and Types::Standard for my class attributes. My efforts always produce a extra ArrayRef that is one level deeper than I need.
As far as I can tell, you have to assign a reference to the attribute once it's marked as a 'Ref' but in doing so I end up with an array reference inside an array reference. Perhaps I want a list type but I don't see one.

Code

#!perl

use v5.22;
use warnings;

use Test::Deep;
use Test::More;

BEGIN {
    package MockObj;

    use Moo;
    use Types::Standard qw(ArrayRef Str);
    use namespace::autoclean;

    has 'files' => (
        # `rpw` would be better as, in practice, 
        # this is only used inside the class
        is => 'rw',   
        isa => ArrayRef[Str],
    );
    1;
};

my $mock = MockObj->new;

my @list = ('string one', 'Different string', 'With feeling');
note explain \@list;
$mock->files( \@list );
my @strings = $mock->files;
note explain \@strings;

cmp_deeply(\@strings, bag(@list));

done_testing;
[download]

Result

# [
#   'string one',
#   'Different string',
#   'With feeling'
# ]
# [
#   [
#     'string one',
#     'Different string',
#     'With feeling'
#   ]
# ]
not ok 1
#   Failed test at t/test-case.t line 31.
# Comparing $data as a Bag
# Missing: 'Different string', 'With feeling', 'string one'
# Extra: 1 reference
[download]

Your enlighenment is much appreciated,

Comment on Assigning to a ArrayRef accessor type Select or Download Code

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Re: Assigning to an ArrayRef accessor type
by Athanasius (Archbishop) on Sep 21, 2020 at 15:15 UTC

Hello tomred, and congratulations on your first post!

MockObj::files is not an array, it’s an array reference. So instead of assigning to an array variable:

my @strings = $mock->files;
[download]

you should assign to a scalar:

my $strings = $mock->files;
note explain $strings;

cmp_deeply($strings, bag(@list));
[download]

which gives the desired test result:

 1:14 >perl 2056_SoPW.pl
# [
#   'string one',
#   'Different string',
#   'With feeling'
# ]
# [
#   'string one',
#   'Different string',
#   'With feeling'
# ]
ok 1
1..1

 1:14 >
[download]

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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Re^2: Assigning to an ArrayRef accessor type

by tobyink (Canon) on Sep 21, 2020 at 17:08 UTC

An alternative to this:

my $strings = $mock->files;
[download]

Would be this:

my @strings = @{ $mock->files };
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Or if you've got a very recent version of Perl:

my @strings = $mock->files->@*;
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Moose also has an optional feature where it can detect if an accessor is called in a list context and return a list instead of a reference, but Moo didn't implement that because it can get confusing to work with.

toby döt ink

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Re^3: Assigning to an ArrayRef accessor type

by tomred (Acolyte) on Sep 22, 2020 at 10:59 UTC

Thank you

[reply]

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