Exercise: Errors

题目内容：

Copy Sqrt function from the earlier exercise and modify it to return an error value.

Sqrt should return a non-nil error value when given a negative number, as it doesn't support complex numbers.

Create a new type

type ErrNegativeSqrt float64

and make it an error by giving it a

func (e ErrNegativeSqrt) Error() string

method such that ErrNegativeSqrt(-2).Error() returns "cannot Sqrt negative number: -2".

Note: A call to fmt.Sprint(e) inside the Error method will send the program into an infinite loop. You can avoid this by converting e first: fmt.Sprint(float64(e)). 

Change your Sqrt function to return an ErrNegativeSqrt value when given a negative number.

练习程序

package mainimport ("fmt""math"
)type ErrNegativeSqrt float64func (e ErrNegativeSqrt) Error() string{return fmt.Sprint("cannot Sqrt negative number ", float64(e))
}func Sqrt(x float64) (float64, error) {z := 1.0if x < 0 {return x, ErrNegativeSqrt(x)}for math.Abs(z*z - x) > 0.00000001 {z -=  (z*z - x) / (2 * z)}return z, nil
}func main() {fmt.Println(Sqrt(2))fmt.Println(Sqrt(-2))
}

运行结果:

1.4142135623746899 
-2 cannot Sqrt negative number -2

学习笔记：本题考察如果利用编写一个Error方法，实现go语言内置error interface中定义的Error方法，从而返回自定义的报错信息。