Unit Access Ramifications e.g. Materialization

[seandenigris]

In v11, there are two properties of units that seemingly make them hard to work with:

1. They are accessed from numerous class-side collections e.g. InternationalSystemOfUnits units >> #litre and USCustomaryUnits units >> #pound
2. Equality is identity-based, except for DerivedUnit and UnitOfAccount

I'm not clear how this can work in practice. For example, say I serialize data including Quantity instances, like recipes with ingredient amounts like 2 tsp. How can this data get materialized? If the data is saved naively, the materialized unit of the quantity will not be the one in the class-side collection, but a copy. Since unit equality is identity-based (i.e. not overridden from the built-in Object implementation), the system will now report false for 2 tsp unit (materialized) == 2 tsp unit (newly created). I suppose a user might decide to take over the responsibility to serialize and materialize and used Aconcagua unit collections, but that seems like an odd requirement for a simple use case.

[gcotelli]

I don't know exactly the fuel internals, but on a quick search, looks like FLGlobalSendCluster can be useful here. What you're describing is a problem that will happen with any instance that's held in some class variable and expect to be unique: a singleton, a well known instance of some class, etc.
What we need to do here is not to serialize the whole instance but somehow a way to lookup it again during the materialization phase.

[seandenigris]

I considered such an approach, but wasn't sure how to go about it since:

1. there is not one global registry to search, but several such sources, possibly split between Aconcagua and other projects
2. It doesn’t seem like any state in the objects records clues to this source

[seandenigris]

The other wrinkle is that Aconcagua's stores of units (e.g. InternationalSystemOfUnits) are not fixed. If the user simply takes responsibility for serialization of the class-side variables, any units added to Aconcagua after that initial save will not be added. This pushes me further down the road considering including state in the unit objects to recreate the unit - something like { InternationalSystemOfUnits. #units. #litre } (or a reification thereof) that can be converted back to InternationalSystemOfUnits units >> #litre. Thoughts?