How to make data arg optional only if cat argument is not 1 ?

export class MyClass<T extends 1 | 2 | 3>{
  constructor(
    public cat: T,
    public data?: T extends 1 ? string[] : undefined,
  ) {
    ...
  }
}

How to make data arg optional only if cat argument is not 1 ?

export class MyClass<T extends 1 | 2 | 3>{
  constructor(
    public cat: T,
    public data?: T extends 1 ? string[] : undefined,
  ) {
    ...
  }
}

• typescript

1 Answer 1

You could go with overloads.

export class MyClass<T extends 1 | 2 | 3> {
  constructor(cat: 1, data: string[]);
  constructor(cat: Exclude<T, 1>);
  constructor(
    public cat: T,
    public data?: string[],
  ) {
    ...
  }
}

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