How to use AnyClass to init an specific class instance in swift3.x

Question

I have seen this question on stackoverflow Here Unfortunately, this answer is not helpful in swift3.x

protocol Effect {

    func des()
}

class A: Effect {

    func des() {
        print("This is A")
    }

    required init() { }
}

class B: Effect {

    func des() {
        print("This is B")
    }

    required init() { }
}

I want to store class A & B in an array

var array = [Effect.Type]()
array.append(A.self)
array.append(B.self)

When I want to get class A & B from array, I get this result

A.self   // __lldb_expr_23.A.Type
A.self.init().des() -> This i A
array[0] // __lldb_expr_23.A.Type
array[0].init().des() -> Error

Error Image

I know I can use this method to init Class A

let a = array[0] as! A.Type
a.init().des() -> This is class A

But if I don't know the class exactly, I cannot init the class by Effect.Type So How to use AnyClass to init an specific class instance without use as! ... in Swift3.x?

Are you wanting to store an array of Types? Or of instances of objects? — Fogmeister, Aug 15 '17 at 08:04
I want to store an array of Types? And then use these Types to init instances of objects — pluto, Aug 15 '17 at 08:19

Martin R · Accepted Answer · 2017-08-15T08:15:00.510

2

You have to add init() as requirement to the protocol definition in order to call it on the array values of type Effect.Type:

protocol Effect {
    init()
    func des()
}

Then everything works as expected:

let array: [Effect.Type] = [ A.self, B.self ]

array[0].init().des() // This is A
array[1].init().des() // This is B

edited Aug 15 '17 at 08:15

answered Aug 15 '17 at 08:08

Martin R

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It works. But why must I add init() in the protocol? Is the reason that Effect.Type cannot Analysis the method init()? – pluto Aug 15 '17 at 08:24
1

@pluto: How else could the compiler know that all types conforming to `Effect` have an `init()` method? – Martin R Aug 15 '17 at 08:25
Ok, I understand – pluto Aug 15 '17 at 08:27

How to use AnyClass to init an specific class instance in swift3.x

1 Answers1