How do I interact with a Perl object that has a hash attribute?

Question

I have a class with several variables, one of which is a hash (_runs):

sub new
{
    my ($class, $name) = @_;
    my $self = {
        _name => $name,
                


        

Answer 1

Might as well take my comments and make a proper answer out of it. I'll illustrate exactly why your sample code failed.

use warnings;
my $self = {
    _name => $name,
    _runs => (),
    _times => [],
};
bless ($self, $class);

use Data::Dump::Streamer; DumpLex $self;

__END__
Odd number of elements in anonymous hash at …

$self = bless( {
    _name             => undef,
    _runs             => '_times',
    "ARRAY(0x88dcb8)" => undef,
}, '…' );

All the elements in the list form the key/value pairs for the hash whose reference is going to be blessed. () is an empty list, so what you're really expressing is the list '_name', $name, '_runs', '_times', []. You can see that _times moves up to become a value, and the reference [] is stringified as hash key. You get the warning because there's no value left for it; this will be automatically coerced to undef. (Always always enable the warnings pragma.)

Now for the guts part: hash values must be a scalar value. Arrays and hashes aren't; but references to them are. Thus:

my $self = {
    _name => $name,
    _runs => {},
    _times => [],
};