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Most explicit stronger typing #8

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Most explicit stronger typing #8

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62 changes: 60 additions & 2 deletions src/project.ts
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
import { LiveObject, Room } from "@liveblocks/client";
import { ElementId, FileFormat } from "./fileFormat";
import { Sketch } from "./elements/sketch";
import { ArcolObjectStore, ObjectChange, ObjectListener, ObjectObserver, StoreName } from "./arcolObjectStore";
import { ArcolObjectFields, ArcolObjectStore, ChangeOrigin, ObjectChange, ObjectListener, ObjectObserver, StoreName } from "./arcolObjectStore";
import { Extrusion } from "./elements/extrusion";
import { Group } from "./elements/group";
import { Level } from "./elements/level";
Expand All @@ -10,9 +10,67 @@ import { generateKeyBetween } from "fractional-indexing";
import { HierarchyObserver } from "./hierarchyMixin";
import { ChangeManager } from "./changeManager";

export type ElementListener = ObjectListener<Element>;
export type ElementObserver = ObjectObserver<Element>;

/**
* A more strongly typed version of {@link ObjectChange}.
*
* It uses mapped types and index access types to produce a union of all the possible changes for
* a given object type.
*
* e.g.
* TypedObjectChange<{ k1: V1, k2: V2, ... }> =
* | { type: "create" | "delete" }
* | { type: "update", property: "k1", oldValue: V1 }
* | { type: "update", property: "k2", oldValue: V2 }
* ...
*/
type TypedObjectChange<T extends ArcolObjectFields> =
| { type: "create" | "delete" }
| { [K in keyof T]: { type: "update", property: K, oldValue: T[K] } }[keyof T]

/**
* A more strongly typed version of {@link ObjectListener} for `Element`. The argument to the
* callback is a single `params` object which repeats the `type` from `obj.type`. This allows
* narrowing both `obj` and `change` based on the `type` of the `Element`.
*
* In more concrete terms, it allows the following to give the desired types:
* ```
* if (params.type === "someElementType") {
* if (params.change.type === "update") {
* // params.change.property is a union of the possible fields of `someElementType`
* if (params.change.property) {
* // params.change.value is the type of the field [params.change.property] in `someElementType`
* }
* }
* }
* ```
*/
type ElementListenerParam =
| { type: "sketch", obj: Sketch, change: TypedObjectChange<FileFormat.Sketch>, origin: ChangeOrigin }
| { type: "extrusion", obj: Extrusion, change: TypedObjectChange<FileFormat.Extrusion>, origin: ChangeOrigin }
| { type: "group", obj: Group, change: TypedObjectChange<FileFormat.Group>, origin: ChangeOrigin }
| { type: "level", obj: Sketch, change: TypedObjectChange<FileFormat.Level>, origin: ChangeOrigin }
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Alternatively

type ElementChangeCreator<T extends Element, F extends FileFormat.Element> =
  | { type: T["type"], obj: T, change: TypedObjectChange<F>, origin: ChangeOrigin }

type ElementListenerChange =
  | ElementChangeCreator<Level, FileFormat.Level>
  | ElementChangeCreator<Sketch, FileFormat.Sketch>
  ...


type ElementListener = (params: ElementListenerParam) => void

// This is just here as a test that our TypeScript types are able to perform the desired narrowing.
function foo(l: ElementListener) {}
foo((params) => {
if (params.type === "sketch") {
const obj: Sketch = params.obj;
if (params.change.type === "update") {
const property: "id" | "type" | "parentId" | "parentIndex" | "translate" | "color" = params.change.property;
if (params.change.property === "translate") {
const old: FileFormat.Vec3 = params.change.oldValue
void old;
}
void property;
}
}
})


class DeleteEmptyExtrusionObserver implements ElementObserver {
private elementsToCheck = new Set<ElementId>();

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