Krux's solution is the most efficient. You can also use inheritance:
import strutils
type
BaseType = ref object of RootObj
StringType = ref object of BaseType
value: string
IntType = ref object of BaseType
value: int
method toString(bt: BaseType): string {.base.} = ""
method toString(st: StringType): string = st.value
method toString(it: IntType): string = $it.value
proc getArg(typeName:string, strValue:string):BaseType=
case typeName:
of "string":
result = StringType(value: strValue)
of "int":
result = IntType(value: parseInt(strValue))
let bt = getArg("int", "777")
echo "ToString: ", toString(bt)
if bt of StringType:
echo("Casting: ", StringType(bt).value)
elif bt of IntType:
echo("Casting: ", IntType(bt).value)
[run it](https://glot.io/snippets/en6i60pzu6)
