exercise-errors.go

package main

import (
	"fmt"
	"math"
)

type ErrNegativeSqrt float64

func (e ErrNegativeSqrt) Error() string {
	return fmt.Sprintf("cannot Sqrt negative number: %v", float64(e))
}

func Sqrt(x float64) (float64, error) {
	if x < 0 {
		return 0.0, ErrNegativeSqrt(x)
	}

	z := float64(1.0)
	for i := 0; i < 10; i++ {
		t := z
		z = z - (z*z-x)/(2*z)
		d := math.Abs(z - t)
		if d < 1e-12 {
			break
		}
	}

	return z, nil
}

https://tour.go-zh.org/methods/20