Universal/heterogeneous maps.
These maps are useful for storing values of arbitrary type in a single map. In order
to recover a value, it must be looked up with exactly the Key.t
it was stored in.
In other words, given different Key.t
's from the same string
, one will not be able
to recover the key stored in the other one.
This is similar to Univ
in spirit.
find
is no longer partial