Short variable declaration and “variable declared and not used” error

Question

I\'ve stumbled across a strange issue where the code below fails to compile:

func main() {
    var val reflect.Value
    var tm time.Time

    if tm, err := time         


        

Answer 1

Your if statement declares a new variable tm that exists only within the scope of the if block and is indeed never used:

if tm, err := time.Parse(time.RFC3339, "2018-09-11T17:50:54.247Z"); err != nil {
    panic(err)
}

In Go, := declares a new variable and initializes it. You probably meant:

func main() {
    var val reflect.Value
    var tm time.Time
    var err error

    // Note the change to normal assignment here instead of :=
    if tm, err = time.Parse(time.RFC3339, "2018-09-11T17:50:54.247Z"); err != nil {
        panic(err)
    }
    val = reflect.ValueOf(tm)

    fmt.Println(val, tm, reflect.TypeOf(tm))
}

The := shortcut operator is demonstrated in the Tour of Go and explained in the Go spec, the latter of which includes:

It is shorthand for a regular variable declaration with initializer expressions but no types:

"var" IdentifierList = ExpressionList .

Scoping is explained in the Go spec as well.