如果一个对象的属性之一可能具有不同的名称，如何对其进行类型保护？

interface Square {
    kind: "square";
    size: number;
}

interface Rectangle {
    kind: "rectangle";
    width: number;
    height: number;
}

type Shape = Square | Rectangle;

function isSquare(shape: Shape): shape is Square {
    return shape.kind === "square";
}

function area(shape: Shape) {
    if (isSquare(shape)) {
        // 在这个if语句块内，TypeScript知道shape是Square类型
        return shape.size * shape.size;
    } else {
        // TypeScript知道shape是Rectangle类型
        return shape.width * shape.height;
    }
}

function getShapeKind(shape: Shape): string {
    if ((shape as Square).kind) {
        return (shape as Square).kind;
    } else {
        return (shape as Rectangle).kind;
    }
}

function hasKind(shape: Shape, kind: string): shape is Shape {
    return shape.kind === kind;
}

function getArea(shape: Shape) {
    if (hasKind(shape, "square")) {
        // TypeScript知道shape是Square类型
        return shape.size * shape.size;
    } else if (hasKind(shape, "rectangle")) {
        // TypeScript知道shape是Rectangle类型
        return shape.width * shape.height;
    }
}