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New to Go, trying to solve Tour of Go, Exercise 56, which is about error handling.

Can the following error handling method can be further improved?

package main

import (
    "fmt"
    "math"
)

type ErrNegativeSqrt float64

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

func Sqrt(f float64) (float64, error) {
    if f > 0 {
        return math.Sqrt(f), nil
    } else {
        return 0, ErrNegativeSqrt(f)
    }
}

func main() {
    fmt.Println(Sqrt(2))
    fmt.Println(Sqrt(-2))
}
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  • \$\begingroup\$ Minor point, but you don't need to wrap the return 0, ErrNegativeSqrt(f) in an else block. The go vet tool would complain about this. \$\endgroup\$ Commented Dec 8, 2013 at 8:29

2 Answers 2

Reset to default
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I would name the error ErrSqrtNegative instead of ErrNegativeSqrt.

Sqrt(0) should not be an error.

In case of error, I would use math.NaN(), ErrSqrtNegative(f) as the return values.

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  • 1
    \$\begingroup\$ Hmm. It looks like the exercise calls for the error to be named ErrNegativeSqrt. \$\endgroup\$ Commented Oct 23, 2013 at 5:34
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For example,

package main

import (
    "fmt"
    "math"
)

type ErrNegativeSqrt float64

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

func Sqrt(f float64) (float64, error) {
    if f < 0 {
        return 0, ErrNegativeSqrt(f)
    }
    const delta = 1e-12
    z := f
    for {
        zz := z
        z -= (z*z - f) / (2 * z)
        if math.Abs(z-zz) < delta {
            break
        }
    }
    return z, nil
}

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

Output:

1.414213562373095 <nil>
0 cannot Sqrt negative number: -2
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  • \$\begingroup\$ Code-only answers do not constitute a review. Please explain how your changes improve the original code. \$\endgroup\$ Commented Jan 28, 2014 at 17:26

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