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ecs: allow Map and Set resources with a default, and symbol-keyed maps #247
Description
Summary
Declaring a resource of type Map or Set is narrow: ReadonlyMap<symbol, unknown> and Resource.Key are rejected ("keyof isn't a declared type"), and a ReadonlySet takes no default.
Case (mecs, @adobe/ecs 0.2.4)
History keeps a note of the values it wrote when it applied an undo/redo, so the finalizer that records resource changes skips them. It is a set of strings ("<index>=<json>"), declared as ReadonlySet<string> with no default; we had wanted ReadonlyMap<Resource.Key, unknown> (key to value) and a default: new Set().
`keyof` isn't a declared type (for the Resource.Key / symbol key)
default isn't of its declared type (for the Set)
We worked around it by encoding keys and values in a string.
Requested
Allow Map/Set (readonly) with a default of the same type, and allow a symbol-typed map key, or document the limits of declared types and why.
Activity
krisnye commentedon Nov 1, 2026
Addressed in #250 (Adobe-Firefly/ecs#9), with one correction to the premise: a
ReadonlySetorReadonlyMapresource needs nodefault. It starts empty in each world. Giving it one now says "…which starts empty in each world: leave its default out".A set or map of what isn't data now registers as a value that isn't data, still starting empty in each world. That covers a symbol,
Resource.KeyorComponent.Key, a class, orunknown, soReadonlyMap<Resource.Key, unknown>works. Symbol keys stay out of data: data crosses threads by structured clone, which refuses symbols, and is saved by schema. So such a map stays on the world's thread and isn't persisted, which suits the history's note.