I also had this problem and I found a workaround for my case.
In this article the author has the same problem
https://www.iphonelife.com/blog/31369/swift-programming-101-generics-practical-guide
So the problem seems to be, that the compiler needs to infer the type of T somehow. But it isn’t allowed to simply use generic< type >(params…).
Normally, the compiler can look for the type of T, by scanning the parameter types because this is where T is used in many cases.
In my case it was a little bit different, because the return type of my function was T. In your case it seems that you haven’t used T at all in your function. I guess you just simplified the example code.
So I have the following function
func getProperty<T>( propertyID : String ) -> T
And in case of, for instance
getProperty<Int>("countProperty")
the compiler gives me the error:
Cannot explicitly specialize a generic function
So, to give the compiler another source of information to infer the type of T from, you have to explicitly declare the type of the variable the return value is saved in.
var value : Int = getProperty("countProperty")
This way the compiler knows that T has to be an integer.
So I think overall it simply means that if you specify a generic function you have to at least use T in your parameter types or as a return type.