In Perl, hashes are typically used for two sorts of purposes: maps (where the hash key acts as an object identifier) and dictionaries (where the hash key acts like a field name). A quick illustration of what I mean…
Let's say you want an attribute to accept a pair of numbers – perhaps a geographic co-ordinates [ 50.873, -0.002 ]. You could constrain the attribute as ArrayRef[Num], but that would accept an arrayref containing a single number, or…
So you have this Moo class, and it turns out what you really need for it is the StrictVersionStr type constraint defined in MooseX::Types::Perl. You could switch the class to Moose, but long term you want to stick with…