Swift: write a function that allocates an instance of (any) class - objective-c

Question

I'm looking for the equivalent of the following Obj-C code in Swift:
- newInstanceOf:(id)classRef {
return [classRef new];
}
and then to use it:
id instance = [whatever newInstanceOf:NSArray.class]
[instance isKindOfClass:NSArray.class] == YES
I have tried using a Swift template:
func newSomething<T>(classRef:T.Type) -> T {
return classRef()
}
I get the error: error: 'T' cannot be constructed because it has no accessible initializers

Answer 1

You could create a protocol to act as a type constraint for objects initializable by a void-argument initializer, and thereafter extend your types of choice to this protocol.
protocol SimplyInitializable {
init()
}
extension Int : SimplyInitializable { }
extension Double : SimplyInitializable { }
extension String : SimplyInitializable { }
struct MyStruct {
var myInt : Int
init() {
myInt = 0
}
}
extension MyStruct : SimplyInitializable { }
func newSomething<T: SimplyInitializable>(classRef: T.Type) -> T {
return classRef.init()
}
/* Examples */
var a = newSomething(Int)
var b = newSomething(Double)
var c = newSomething("".dynamicType)
var d = newSomething(MyStruct)
var e = newSomething(a.dynamicType)
print(a.dynamicType) // Int
print(b.dynamicType) // Double
print(c.dynamicType) // String
print(d.dynamicType) // MyStruct
print(e.dynamicType) // Int

Answer 2

Actually in Swift, not all classes are guaranteed to have an init() initializer. It can work with NSObject classes though because NSObject does have that requirement.
func newInstanceOf<T:NSObject>(aClass:T.Type) -> NSObject
{ return aClass.init() }
let string = newInstanceOf(NSString) // ""
let date = newInstanceOf(NSDate) // 2016-01-15 05:27:29 +0000