I have classes Alpha and Berry:
class Alpha { }
class Berry : Alpha { }
I have a function that using inheritance within it's generic:
func myFunc<T : Alpha>(v:T) -> T {
return T()
}
I call myFunc like this:
myFunc(Berry())
In my project, the object that gets returned is of type Alpha, and not of type Berry. Is this is a bug in the compiler, or if this is simply something I'm misunderstanding about generics?
What you trying to achieve is passing an instance of Berry and getting another instance of Berry?
If so, following code should work:
class Alpha {
required init() { } // ← YOU NEED THIS
func printme() {
println("I'm alpha")
}
}
class Berry : Alpha {
override func printme() {
println("I'm berry")
}
}
func myFunc<T:Alpha>(v:T) -> T {
return v.dynamicType()
}
// This also works:
/*
func myFunc<T: Alpha>(v:T) -> T {
return (T.self as T.Type)()
}
*/
let a = myFunc(Berry())
a.printme() // -> I'm berry
required init() { } is necessary to ensure all classes derived from Alpha have init() initializer.
Here is related Q/A: Swift generics not preserving type
If what you want is passing Berry as a type and get new instance of Berry, try this:
class Alpha {
required init() { }
func printme() {
println("alpha")
}
}
class Berry : Alpha {
override func printme() {
println("berry")
}
}
func myFunc<T:Alpha>(v:T.Type) -> T {
return v()
}
let a = myFunc(Berry)
a.printme()
