porton porton - 2 months ago 5
Perl Question

"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?

Answer

This can be solved by adding:

sub BUILD {
  my ($self, $args) = @_;

  $self->base($self->base_builder);
  foreach my $Key (keys %$args) {
    $self->$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) = @_;

  $self->base($self->base_builder);
  foreach my $Key (keys %$args) {
    $self->$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};
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