Since these will live for the lifetime of the process, it is worth freezing them on creation to improve lookup performance. If the dictionaries were iterated, change to an immutable array instead to preserve the order.
* ResourceType trait has been removed.
* Simulation-related data is now defined on the
ResourceLayer (which mods can subclass/replace).
* Support non-money resources by moving the resource
values to the PlayerResources trait.
* Allow mods to disable the neighbour density override
and instead always use the map-defined densities.
* Allow mods to define their own resource placement
logic (e.g. allow resources on slopes) by subclassing
(Editor)ResourceLayer.
* Improve ability to subclass/override ResourceRenderer
by exposing more virtual methods.
