25 lines
599 B
TypeScript
25 lines
599 B
TypeScript
// @strict: true
|
|
interface Cat {
|
|
type: 'cat';
|
|
canMeow: true;
|
|
}
|
|
|
|
interface Dog {
|
|
type: 'dog';
|
|
canBark: true;
|
|
}
|
|
|
|
type Animal = Cat | Dog;
|
|
|
|
declare function assertEqual<T>(value: any, type: T): asserts value is T;
|
|
|
|
const animal = { type: 'cat', canMeow: true } as Animal;
|
|
assertEqual(animal.type, 'cat' as const);
|
|
|
|
animal.canMeow; // since is cat, should not be an error
|
|
|
|
const animalOrUndef = { type: 'cat', canMeow: true } as Animal | undefined;
|
|
assertEqual(animalOrUndef?.type, 'cat' as const);
|
|
|
|
animalOrUndef.canMeow; // since is cat, should not be an error
|