A Tour of Go - Exercise: Errors

exercise-errors.go

// Copy your 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)). Why?
//
// Change your Sqrt function to return an ErrNegativeSqrt value when given a negative number.
package main

import (
	"fmt"
	"math"
)

type ErrNegativeSqrt float64

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

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

	z := (x / 2)
	last_z := z
	change := 1.0
	minimum_change := 0.000000000000001
	iteration := 0

	for change > minimum_change {
		z -= (z*z - x) / (2 * z)
		change = math.Abs(last_z - z)
		last_z = z
		iteration++
	}

	fmt.Println("This answer took ", iteration, " loop iterations")
	return z, nil
}

func main() {
	fmt.Println(Sqrt(2))
	fmt.Println(Sqrt(-2))
}