A Tour of Go chapter 56
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.
Example
package main import ( "fmt" "math" ) type ErrNegativeSqrt float64 func (err ErrNegativeSqrt) Error() string { return fmt.Sprintf("cannot Sqrt negative number: %v", float64(err)) } func Sqrt(f float64) (float64, error) { z := f / 2 if f < 0 { return 0, ErrNegativeSqrt(f) } var prez float64 = 0 for math.Abs(z - prez) > 1e-10 { prez = z z = z - (z * z - f) / (z * 2) } return z, nil } func main() { fmt.Println(Sqrt(2)) fmt.Println(Sqrt(-2)) }