How Can I Safely Pass Nil Interface Values Using Go Reflection?

Passing Nil Values as Interfaces via Reflection

Reflecting upon interfaces presents the challenge of passing nil values effectively. Consider the following function:

func f(e error) {
    if e == nil {
        fmt.Println("YEY! NIL") // Aim for this
    } else {
        fmt.Println("NOT NIL :(")
    }
}

If you attempt to pass a nil value to the function via reflection using the below code, it will result in a panic:

nilArg := reflect.Zero(reflect.TypeOf((error)(nil)))

Don't despair! To bypass the issue, utilize the expression reflect.TypeOf((*error)(nil)).Elem() to obtain the reflect.Type for the interface error. This trick involves passing a non-interface value to reflect.TypeOf() and using reflect.Elem() to derive the desired type.

For the nilArg construction, employ the following:

nilArg := reflect.Zero(reflect.TypeOf((*error)(nil)).Elem())

Enjoy a working playground example to solidify your understanding.

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