[swift-users] Detect if a generic type is numeric

[davelist at mac.com]

> On Sep 21, 2017, at 3:58 PM, V T via swift-users <swift-users at swift.org> wrote:
> 
> Hi there!
> 
> Is there a best way to check if a given type conforms to numeric protocol (Integer or FP) at runtime?
> 
> func checkNumeric<T>(_ value: T) {
> 	/* return true if vaiue is Integer or FP */
> 	/* this will not compile: */
> 	if value is Numeric {
> 		
> 	}
> }
> 
> Best regards!
> 
> VT
> 

I think the way to do it is to try casting as the type, but you can't use "as? Numeric" as you get:

 error: protocol 'Numeric' can only be used as a generic constraint because it has Self or associated type requirements

but you could check for each specific numeric type such as:

func checkNumeric<T>(_ value: T) {
    if (value as? Int != nil) || (value as? Float != nil) {
        print("numeric")
    } else {
        print("not numeric")
    }
}

checkNumeric(3)
checkNumeric(3.0)
checkNumeric("3")

HTH,
Dave