How to check generic class type is array?

Question

I want to check whether the generic class type is an Array:

func test<T>() -> Wrapper<T> {
  let isArray = T.self is Array<Any>
  ... 
}

But it warns

Cast from 'T.type' to unrelated type 'Array' always fails

How can I solve this problem?

added: I've uploaded my codes to Gist. https://gist.github.com/nallwhy/6dca541a2d1d468e0be03c97add384de

What I want to do is to parse json response according to it's an array of model or just one model.


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| swift   | swift3   2017-01-07 07:01 2 Answers

Answers ( 2 )

  1. 2017-01-07 07:01

    You are not passing any argument, so there is no type and a generic function does not make sense. Either remove the generic type:

    func() {}
    

    or, if you want to pass an argument:

    let array = ["test", "test"]
    func test<T>(argument: T) {
        let isArray = argument is Array<Any>
        print(isArray)
    }
    
    test(argument: array)
    

    Prints: true

  2. 2017-01-07 12:01

    As commentator @Holex says, you can use Any. Combine it with Mirror and you could, for example, do something like this:

    func isItACollection(_ any: Any) -> [String : Any.Type]? {
        let m = Mirror(reflecting: any)
        switch m.displayStyle {
        case .some(.collection):
            print("Collection, \(m.children.count) elements \(m.subjectType)")
            var types: [String: Any.Type] = [:]
            for (_, t) in m.children {
                types["\(type(of: t))"] = type(of: t)
            }
            return types
        default: // Others are .Struct, .Class, .Enum
            print("Not a collection")
            return nil
        }
    }
    
    func test(_ a: Any) -> String {
        switch isItACollection(a) {
        case .some(let X):
            return "The argument is an array of \(X)"
        default:
            return "The argument is not an array"
        }
    }
    
    test([1, 2, 3]) // The argument is an array of ["Int": Swift.Int]
    test([1, 2, "3"]) // The argument is an array of ["Int": Swift.Int, "String": Swift.String]
    test(["1", "2", "3"]) // The argument is an array of ["String": Swift.String]
    test(Set<String>()) // The argument is not an array
    test([1: 2, 3: 4]) // The argument is not an array
    test((1, 2, 3)) // The argument is not an array
    test(3) // The argument is not an array
    test("3") // The argument is not an array
    test(NSObject()) // The argument is not an array
    test(NSArray(array:[1, 2, 3])) // The argument is an array of ["_SwiftTypePreservingNSNumber": _SwiftTypePreservingNSNumber]
    
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