go语言Exercise: Errors

Copy your

Sqrt

function from the earlier exercises 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.Print(e)

inside the

Error

method
will send the program into an infinite loop. You can avoid this by converting

e

first:

fmt.Print(float64(e))

.
Why?
Change your

Sqrt

function to return an

ErrNegativeSqrt

value
when given a negative number.
package main

import (

"fmt"

)

type ErrNegativeSqrt float64

func (e ErrNegativeSqrt) Error() string{

return fmt.Sprintf("cantnot Sqrt negative number: %v", float64(e))

}

func Sqrt(f float64) (float64, error) {

if f < 0 {

return 0, ErrNegativeSqrt(f)

}

z := f

for i := 0; i < 10; i++ {

z = (z + f/z)/2

}

return z, nil

}

func main() {

if value, err := Sqrt(-2); err != nil {

fmt.Println(err)

} else {

fmt.Println(value)

}

if value, err := Sqrt(2); err != nil {

fmt.Println(err)

} else {

fmt.Println(value)

}

}