TypeScript声明方法返回类型是类或子类的实例类型

class Animal {
    name: string;
    constructor(name: string) {
        this.name = name;
    }
}

class Dog extends Animal {
    breed: string;
    constructor(name: string, breed: string) {
        super(name);
        this.breed = breed;
    }
}

class Cat extends Animal {
    color: string;
    constructor(name: string, color: string) {
        super(name);
        this.color = color;
    }
}

function createAnimal(type: 'Dog' | 'Cat', name: string, extraInfo?: string): Animal {
    switch (type) {
        case 'Dog':
            return new Dog(name, extraInfo!);
        case 'Cat':
            return new Cat(name, extraInfo!);
        default:
            throw new Error('Invalid animal type');
    }
}

const dog = createAnimal('Dog', 'Buddy', 'Golden Retriever');
const cat = createAnimal('Cat', 'Whiskers', 'Black');

console.log(dog); // Dog { name: 'Buddy', breed: 'Golden Retriever' }
console.log(cat); // Cat { name: 'Whiskers', color: 'Black' }

function createAnimal(type: 'Dog' | 'Cat', name: string, extraInfo?: string): Animal {
    // ...
}

function createAnimal(type: 'Dog' | 'Cat', name: string, extraInfo?: string): Animal {
    switch (type) {
        case 'Dog':
            return new Dog(name, extraInfo!); // 确保返回 Dog 类型
        case 'Cat':
            return new Cat(name, extraInfo!); // 确保返回 Cat 类型
        default:
            throw new Error('Invalid animal type');
    }
}