How in Swift specify type constraint to be enum?

Question

I want to specify a type constraint that the type should be a raw value enum:

enum SomeEnum: Int {
  case One, Two, Three
}

class SomeProtocol

        

Answer 1

AFAIK, Swift does not support type constraint to be specified with enums.

Cited from Swift Manual

Type Constraint Syntax

You write type constraints by placing a single class or protocol constraint after a type parameter’s name, separated by a colon, as part of the type parameter list. The basic syntax for type constraints on a generic function is shown below (although the syntax is the same for generic types):

Strictly limited to a class or protocol unless there's some hidden features which is not mentioned in manual. As far as I tested, struct or enum are all prohibited by the compiler.

enum Test1 : Int
{
    case AAA = 0
}

func test1f(a: Test1) {}       //  error: Inheritance from non-protocol, non-class type 'Test1'

struct Test2
{
    var aaa:Int =   0
}

func test2f(a: Test2) {}       //  error: Inheritance from non-protocol, non-class type 'Test1'


class Test3
{
}

func test3f(a: Test3) {}       //  OK