swift - Cannot explicitly specialize a generic function

Question

I have issue with following code:

func generic1<T>(name : String){
}

func generic2<T>(name : String){
     generic1<T>(name)
}

the generic1(name) result to compiler error "Cannot explicitly specialize a generic function"

Is any way to avoid this error? I can't change signature of generic1 function, therefore it should be (String) -> Void

Answer 1

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.