go語言Exercise: Errors

這是一個建立於 的文章，其中的資訊可能已經有所發展或是發生改變。

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)
}
}