How can I convert custom type to interface{} and then to base type (ex. uint8)?
I can't use direct cast like uint16(val.(Year)) because I may not know all custom types, but I can determinate base types (uint8, uint32,...) in runtime
There are many custom types (usually used as enums) based on numeric:
ex:
type Year uint16
type Day uint8
type Month uint8
and so on...
The question is about type casting from interface{} to base types:
package main
import "fmt"
type Year uint16
// ....
//Many others custom types based on uint8
func AsUint16(val interface{}) uint16 {
return val.(uint16) //FAIL: cannot convert val (type interface {}) to type uint16: need type assertion
}
func AsUint16_2(val interface{}) uint16 {
return uint16(val) //FAIL: cannot convert val (type interface {}) to type uint16: need type assertion
}
func main() {
fmt.Println(AsUint16_2(Year(2015)))
}
You can accomplish this by using the reflect package:
package main
import "fmt"
import "reflect"
type Year uint16
func AsUint16(val interface{}) uint16 {
ref := reflect.ValueOf(val)
if ref.Kind() != reflect.Uint16 {
return 0
}
return uint16(ref.Uint())
}
func main() {
fmt.Println(AsUint16(Year(2015)))
}
Depending on your situation, you may want to return (uint16, error), instead of returning the empty value.
Why did you include Year in the question? Are you hoping to convert arbitrary things into Years, or convert Years into uint16s?
If I assume you meant the latter case, then it would be better to use a method
func (y Year) AsUint16() uint16 {
return uint16(y)
}
which doesn't need any type assertions or reflection.