How to create and set primitive in Golang using reflect

Question

I want to test how my function setFieldValue() works.

func main() {

    value := uint64(0x36)
    resType := reflect.TypeOf(uint8(0))
    expectedRes := uint8(0x36)

    res := uint8(0)
    setFieldValue(reflect.ValueOf(&res).Elem(), resType.Kind(), value)

    if res == expectedRes {
        fmt.Println("voila")
    } else {
        fmt.Println("nuts")
    }
}

func setFieldValue(field reflect.Value, fieldKind reflect.Kind, fieldValue uint64) {
    switch fieldKind {
    case reflect.Uint8:
        field.SetUint(fieldValue)
    }
}

But I don't want res variable also has type TypeOf(uint8(0)) . If I create res as

        res := reflect.New(resType)
        setFieldValue(res, resType.Kind(), value)

it doesn't work because res is unaddressable.

What is the correct way to create variable using reflect and then to set its value in some func?

Or how can I get the instance of newly created variable?

Answer 1

reflect.New returns a reflect.Value that represents a pointer , the pointer itself is not addressable and it's also not what you want to set the value to. What's addressable however is the value to which the pointer points and that's also what you want to set the provided value.

You can use res.Elem() to dereference the pointer.

func main() {
    value := uint64(0x36)
    resType := reflect.TypeOf(uint8(0))
    expectedRes := uint8(0x36)

    res := reflect.New(resType)
    setFieldValue(res.Elem(), resType.Kind(), value)

    if res.Elem().Interface() == expectedRes {
        fmt.Println("voila")
    } else {
        fmt.Println("nuts")
    }
}