Go error handling using switch statement to "pattern match" against return value(s) of function.

errorhandling.go

package main

import "fmt"

// Error
type notSquared struct {
    number int
}

func (e notSquared) Error() string {
    return fmt.Sprintf("Can't square %v for some inexplicable reason?", e.number)
}

// We square? Only to a point...
func square(x int) (int, error) {
    // We can't even begin to compute integers this large
    if x > 10 {
        return 0, notSquared{x}
    }

    return x * x, nil
}

func main() {
    // Loop over some numbers and square them, but watch out for errors!
    for i := 0; i < 42; i++ {

	// Variables scoped to switch expression, can be used in case statements.
        total, err := square(i); switch {

        // Handle error case
        case err != nil:
            panic(err)

        // Numbers that boggle our minds
        case total < 10:
            fmt.Println("such numbers", total)

        default:
            fmt.Println("wow")
        }
    }
}