在Typescript中使用布尔值区分联合

interface Circle {
    isCircle: true;
    radius: number;
}

interface Square {
    isCircle: false;
    sideLength: number;
}

type Shape = Circle | Square;

function getArea(shape: Shape): number {
    if (shape.isCircle) {
        // TypeScript 知道 shape 是 Circle
        return Math.PI * shape.radius * shape.radius;
    } else {
        // TypeScript 知道 shape 是 Square
        return shape.sideLength * shape.sideLength;
    }
}

// 示例用法
const myCircle: Circle = { isCircle: true, radius: 5 };
const mySquare: Square = { isCircle: false, sideLength: 10 };

console.log(getArea(myCircle)); // 输出: 78.53981633974483
console.log(getArea(mySquare)); // 输出: 100

interface Car {
    isCar: true;
    numberOfDoors: number;
}

interface Bike {
    isCar: false;
    hasPedals: boolean;
}

type Vehicle = Car | Bike;

function describeVehicle(vehicle: Vehicle): string {
    if (vehicle.isCar) {
        return `This car has ${vehicle.numberOfDoors} doors.`;
    } else {
        return `This bike ${vehicle.hasPedals ? 'has' : 'does not have'} pedals.`;
    }
}

// 示例用法
const myCar: Car = { isCar: true, numberOfDoors: 4 };
const myBike: Bike = { isCar: false, hasPedals: true };

console.log(describeVehicle(myCar)); // 输出: This car has 4 doors.
console.log(describeVehicle(myBike)); // 输出: This bike has pedals.