不使用类型守卫时，可以使用其他方式对对象进行类型检查，例如使用类型断言或使用类型判断函数。

使用类型断言：

interface Circle {
  radius: number;
}

interface Square {
  sideLength: number;
}

function calculateArea(shape: Circle | Square): number {
  if ((shape as Circle).radius) {
    return Math.PI * (shape as Circle).radius ** 2;
  } else if ((shape as Square).sideLength) {
    return (shape as Square).sideLength ** 2;
  } else {
    throw new Error("Invalid shape");
  }
}

const circle: Circle = { radius: 5 };
console.log(calculateArea(circle)); // Output: 78.53981633974483

const square: Square = { sideLength: 5 };
console.log(calculateArea(square)); // Output: 25

使用类型判断函数：

interface Circle {
  radius: number;
}

interface Square {
  sideLength: number;
}

function isCircle(shape: Circle | Square): shape is Circle {
  return (shape as Circle).radius !== undefined;
}

function calculateArea(shape: Circle | Square): number {
  if (isCircle(shape)) {
    return Math.PI * shape.radius ** 2;
  } else {
    return shape.sideLength ** 2;
  }
}

const circle: Circle = { radius: 5 };
console.log(calculateArea(circle)); // Output: 78.53981633974483

const square: Square = { sideLength: 5 };
console.log(calculateArea(square)); // Output: 25

这些方法虽然没有使用类型守卫，但仍然可以对对象进行类型检查和类型转换。但是需要注意的是，使用类型守卫可以提供更好的类型推断和代码可读性。