Prefer an object over a hash, whenever the keys are significant

In general, any time you're working with a hash that has specific keys
(e.g. accessed with a literal), you've likely got an object wanting to
get out, even if it's just a struct with no other methods. The biggest
upside is more meaningful errors if you have a typo, since the default
behavior of a hash is to return nil. Cases where you don't care about
specific keys (e.g. using a hash to memoize a single argument method)
are fine.
Yeah, I was trying to convey that the value object should be an independent class as opposed to arrays and hashes which are built in and not shuttled away. Maybe that's implied and we can remove the word "named".