（二十五）interface 类继承

interface Product {
    title: string
    price: number
}

// 继承上面的属性, 然后在添加自己独有的属性
interface Tshirt extends product {
    size: 'S' | 'L' | 'M'
}

let product: Product = {
    title: '牛仔裤',
    price: 100,
    size: 'M'
}