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

[Glenn L. Austin]

> On Oct 1, 2017, at 8:56 AM, Dave Reed via swift-users <swift-users at swift.org> wrote:
> 
> 
>> 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")

You can also use the 'is' operator, as in 'value is Int || value is Float || value is Double'

-- 
Glenn L. Austin, Computer Wizard, AustinSoft.com

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