The above replies gave the answer. Here's a little more context:

sub new
{
    my $proto = shift;
    my $class = ref($proto) || $proto;
    my $self = { };
    $self->{token} = { a => 5 };
    # equivalent to $self->{token} = \%( a => 5 );
    return bless($self, $class);
}
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Minor changes required to your accessors:

sub set_token
{
       my $self = shift;
       $self->{token}{$_[0]} = $_[1];
}

sub get_token
{
       my $self = shift;
       return $self->{token}{$_[0]};
}

sub get_token_keys
{
       my $self = shift;
       return keys %{$self->{token}};
}
[download]

Take out the single quotes, especially around the things you need to evaluate (such as $_[0]). Perl used to require quotes on those keys which are barewords, but does not anymore.

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