Skip to content

Change in generic behavior between 3.0.1 and >=3.1.1 #27895

Closed
@chrisbouchard

Description

@chrisbouchard

TypeScript Version: 3.2.0-dev.20181011
This code worked in 3.0.1, and is broken >=3.1.1.

Search Terms:
"is not assignable to type"

Code

export interface Entity {
    id: number | string;
}

export type IdOf<E extends Entity> = E['id'];

export interface EntityState<E extends Entity> {
    ids: IdOf<E>[];
    entities: { [key: string]: E, [key: number]: E };
}


export function getAllEntities<E extends Entity>(state: EntityState<E>): E[] {
    const { ids, entities } = state;
    return ids.map(id => entities[id]);
}

export function getEntity<E extends Entity>(id: IdOf<E>, state: EntityState<E>): E | undefined {
    const { ids, entities } = state;

    if (!ids.includes(id)) {
        return undefined;
    }

    return entities[id];
}

For completeness, I'll just mention that I intend for users to create subinterfaces of Entity and EntityState for their domain types (like @ngrx/entity), overriding id to be a more restrictive type. This is why the IdOf type is important. E.g.,

interface Task extends Entity {
    id: string;
    due: Date;
    title: string;
}

interface TaskState extends EntityState<Task> {
    // Inherits EntityState#ids as string[]
    currentTask?: string;
}

Expected behavior:
The code compiles without error.

Actual behavior:

BUILD ERROR
projects/entity/src/lib/entity-state.utils.ts(13,5): error TS2322: Type '{ [key: string]: E; [key: number]: E; }[E["id"]][]' is not assignable to type 'E[]'.
  Type '{ [key: string]: E; [key: number]: E; }[E["id"]]' is not assignable to type 'E'.
    Type 'Entity' is not assignable to type 'E'.
projects/entity/src/lib/entity-state.utils.ts(23,5): error TS2322: Type '{ [key: string]: E; [key: number]: E; }[E["id"]]' is not assignable to type 'E | undefined'.
  Type 'Entity' is not assignable to type 'E'.
    Type '{ [key: string]: E; [key: number]: E; }[E["id"]]' is not assignable to type 'E'.
      Type 'Entity' is not assignable to type 'E'.

Playground Link:
Playground Link

Related Issues:
I did not find any that seemed similar, but I'm also unsure what the actual underlying problem is. I did ask on StackOverflow, and they suggested I ask here.

Metadata

Metadata

Assignees

Labels

BugA bug in TypeScriptDomain: Indexed Access TypesThe issue relates to accessing subtypes via index accessFixedA PR has been merged for this issue

Type

No type

Projects

No projects

Relationships

None yet

Development

No branches or pull requests

Issue actions