# this class stringifies even though "" is not directly overloaded
{
  "0+" => {
    class => "ICanStringify",
    code => sub { ... },
    code_name => "ICanStringify::__ANON__",
  },
  "fallback" => { class => "ICanStringify", value => undef },
}
# this class does not stringify
{
  "0+" => {
    class => "OnlyANumber",
    code => sub { ... },
    code_name => "OnlyANumber::__ANON__",
  },
  "fallback" => { class => "OnlyANumber", value => 0 },
}