string "ddd" not assignable to type '"ddd" | "dddd"'

[selfisekai]

TypeScript Version: 3.6.0-dev.20190711

Search Terms: string not assignable to type string

Code

export class BaseChannel {
  type: 'text' | 'voice' | 'direct';
}

export class TextChannel extends BaseChannel {
  type = 'text';
}

Expected behavior: assign successfully

Actual behavior: TS2416 error: Property 'type' in type 'TextChannel' is not assignable to the same property in base type 'BaseChannel'. Type 'string' is not assignable to type '"text" | "voice" | "direct"'.

Playground Link: ⛓️

Related Issues: did not find any

[orta]

This is an interesting case of the widening of 'text' into string inside a mutable location.

While this is being discussed, this.type inside the constructor works:

export class BaseChannel {
  type: 'text' | 'voice' | 'direct';
}

export class TextChannel extends BaseChannel {
  // type = 'text';

  constructor() {
    super()
    this.type = 'text'
  }
}

playground link

[AnyhowStep]

Or,

export class BaseChannel {
  type: 'text' | 'voice' | 'direct';
}

export class TextChannel extends BaseChannel {
  type = 'text' as const;
}

Playground

[DanielRosenwasser]

See #32082 (also #340, #1373, #5749, #6118, #10570, #16944, #23911).

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.