perlattributesmoosemoo

"Connecting" a Moo object with a hash


In my real code I want to "synchronize" a Moo (or Moose if Moo won't work) object with a hash (in reality a tied hash), so that reading a property of the Moo object would read the corresponding value from the hash and writing a property of the Moo object would store into the hash.

The following is a simplified code:

#!/usr/bin/perl

use feature qw(say);

package X;
use Moo;
use Data::Dumper;

my $BusinessClass = 'X';

has 'base' => (is => 'rw', builder => 'base_builder');

sub base_builder {
  return {};
}

foreach my $Key (qw(a b c)) {
  {
    no strict 'refs';
    *{"${BusinessClass}::$Key"} = sub {
      if (@_ == 2) {
        return $_[0]->base->{$Key} = $_[1];
      } else {
        return $_[0]->base->{$Key};
      }
    };
    has $Key => ( is        => 'rw',
                  lazy      => 0,
                  required  => 0,
                  reader => "${BusinessClass}::_access1_$Key",
                  writer => "${BusinessClass}::_access2_$Key",
                );
  }
}

my $obj = X->new(a=>123, b=>456);
print Dumper $obj->base;
$obj->c(789);
print Dumper $obj->base;

The trouble is that attributes passed to new function are not stored in the has $obj->base (but they should be). In the above code example the attribute c is properly stored as it should, but a and b are not stored into the hash. This is a bug.

What are good ways to handle this situation?


Solution

  • This can be solved by adding:

    sub BUILD {
      my ($self, $args) = @_;
    
      foreach my $Key (keys %$args) {
        $self->base->{$Key} = $args->{$Key};
        my $clearer = "_clear_local_$Key";
        $self->$clearer();
      }
    }
    

    Complete code:

    #!/usr/bin/perl
    
    use feature qw(say);
    
    package X;
    use Moo;
    use Data::Dumper;
    
    my $BusinessClass = 'X';
    
    has 'base' => (is => 'rw', builder => 'base_builder');
    
    sub base_builder {
      return {};
    }
    
    sub BUILD {
      my ($self, $args) = @_;
    
      foreach my $Key (keys %$args) {
        $self->base->{$Key} = $args->{$Key};
        my $clearer = "_clear_local_$Key";
        $self->$clearer();
      }
    }
    
    foreach my $Key (qw(a b c)) {
      {
        no strict 'refs';
        *{"${BusinessClass}::$Key"} = sub {
          if (@_ == 2) {
            return $_[0]->base->{$Key} = $_[1];
          } else {
            return $_[0]->base->{$Key};
          }
        };
        has $Key => ( is        => 'rw',
                      lazy      => 0,
                      required  => 0,
                      reader => "${BusinessClass}::_access1_$Key",
                      writer => "${BusinessClass}::_access2_$Key",
                      clearer => "_clear_local_$Key",
                    );
      }
    }
    
    my $obj = X->new(a=>123, b=>456);
    print Dumper $obj->base;
    $obj->c(789);
    print Dumper $obj->base;
    
    print Dumper {%$obj};