How the internal structure of the object is organised shouldn't influence how it's indexed. If you later changed the object to

bless $class, [ @_ ];
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you still want to index it the same way. So, either use the individual accessors:

$e->index( index => $index,
           type  => $type,
           id    => $id,
           body  => {
               head    => $object->head,
               opinion => $object->opinion,
               result  => $object->result,
           },
);
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or, create a method for the object to dump a structure to index:

sub hashify {
    my $self = shift;
    return { %$self }
}
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which you can later (after converting to the array implementation) change to

my @attributes = qw( head opinion result );
sub hashify {
    my $self = shift;
    return { map { $attributes[$_] => $self->[$_] } 0 .. $#$self }
}
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Update: Note that hashify creates a shallow copy, i.e. it doesn't clone nested references.