anchor.diff:              callback evt store
           boxableCallback :> obj
   
  -    member this.RegisterEntityInternal archetypeId comps entityRef =
  +    member private this.RegisterEntityInternal archetypeId comps entityRef =
           let archetype =
               match archetypes.TryGetValue archetypeId with
               | (true, archetype) -> archetype
  
positive.code: open System.Threading.Tasks
  open Prime
  
  // TODO: 3D: make sure to use TryAdd in the appropriate places.
  // TODO: 3D: create try functions where applicable and do error-checking where not.
  
  /// Allows a value to always pass as equal with another of its same type.
  type [<CustomEquality; NoComparison; Struct>] 'a AlwaysEqual =
  
negative.code:             | Extra (name, ty, _) ->
                  let storeType = storeTypeGeneric.MakeGenericType [|ty|]
                  let store = Activator.CreateInstance (storeType, name) :?> Store
                  stores.[name] <- store
              | _ -> ()
  
      member this.Id = archetypeId
  