package PseudoHash;

use strict;
use warnings;

use List::Util qw/max/;

# Constructor
# Params:
#   $self   = Existing object reference or package
#   @fields = Field names to be created in the new pseudo hash
# Returns:
#   A new blessed object
sub new {
  my ($self, @fields) = @_;

  my ($class, $layout) = do {
    if (my $class = ref $self) {
      ($class, $self->[0]);
    }
    else {
      ($self, {});
    }
  };

  if (@fields > 0) {
    $layout = { %$layout };
    my $offset = max(0, values %$layout) + 1;

    foreach my $field (@fields) {
      $layout->{$field} = $offset++;
    }
  }

  bless [ $layout ], $class;
}

# Accesses a field of the pseudo hash by name
# Params:
#   $self  = Reference to the pseudo hash
#   $field = Name of the field
# Returns:
#   An lvalue representing the field
sub field : lvalue {
  my ($self, $field) = @_;

  my $offset = $self->[0]->{$field};
  die "No such field '$field' in $self" unless (defined $offset);

  $self->[$offset];
}