How to create an array of classes and instance objects with it in Swift?

Question

I tried to ask this question previously but didn't clearly express my question, so I'll try again here. I also noticed a very similar sounding question, but it is asking for something entirely different.

I have the following code:

class Base {
    func launch(code1: Int, code2: Int) { ... }
}

class A: Base {}
class B: Base {}
class C: Base {}

let classes = [A.self, B.self, A.self, B.self, C.self]
for cls in classes {
    let obj = ???
}

I would like to instantiate an object of type cls inside the loop and do something with it. I might have duplicates inside the array, as shown. What do I put in place of the ??? to be able to instantiate the proper objects?

R Menke · Accepted Answer · 2018-02-27 10:52:02Z

6

All you need is a required init, some way to create an instance that will be shared between all Types you want this to work for. A protocol that holds an init method will do fine.

Obviously this works simplest when the init does not require parameters.

Downside is that you do need to downcast the resulting instances.

protocol ZeroParamaterInit {
    init()
}

class Base : ZeroParamaterInit {
    func launch(code1: Int, code2: Int) {  }
    required init() {

    }
}

class A: Base {}
class B: Base {}
class C: Base {}

let classes : [ZeroParamaterInit.Type] = [A.self,B.self]
var instances : [Any] = []

for cls in classes {

    let instance = cls.init()
    instances.append(instance)

}

for instance in instances {

    if let test = instance as? A {
        print("A")
    }
    if let test = instance as? B {
        print("B")
    }
    if let test = instance as? C {
        print("C")
    }
}

edited Feb 27, 2018 at 10:52

answered Dec 1, 2015 at 18:33

R Menke

8,4294 gold badges40 silver badges64 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Peyman · Accepted Answer · 2015-12-01 17:48:27Z

0

Alright, you'll love this link: http://ijoshsmith.com/2014/06/05/instantiating-classes-by-name-in-swift/

It walks you through the Swift library Obj ectFactory:

https://github.com/ijoshsmith/swift-factory

You really can't do this in Swift. You can, however, do it in Objective-C so you can simply write a wrapper that exposes a Swift interface where behind the scenes, actual object creation is done in Objective-C. That library is exactly what you're looking for.

You'd need to create a ObjectFactory like this:

let factory = ObjectFactory<MyClass>

Then you can instantiate an instance of MyClass like:

let myClass1 = factory.createInstance(className: "MyClassName")

answered Dec 1, 2015 at 17:48

Peyman

3,0971 gold badge35 silver badges70 bronze badges

Comments

user3441734 · Accepted Answer · 2015-12-01 19:01:41Z

import Foundation

class Base {}

class A: Base { var i: Int = 1 }
class B: Base { var i: String = "bravo" }
class C: Base { var i: Bool = true }

let classes = [A.self, B.self, A.self, B.self, C.self]

for cls in classes {
    var obj: Base? {
        switch cls {
        case is A.Type:
            return A()
        case is B.Type:
            return B()
        case is C.Type:
            return C()
        default:
            return nil
        }
    }
    dump(obj)
}


/*
▿ A
    ▿ Some: A #0
    - super: Base
    - i: 1
▿ B
    ▿ Some: B #0
    - super: Base
    - i: bravo
▿ A
    ▿ Some: A #0
    - super: Base
    - i: 1
▿ B
    ▿ Some: B #0
    - super: Base
    - i: bravo
▿ C
    ▿ Some: C #0
    - super: Base
    - i: true
*/

this is very close to R Menke solution ...

Collectives™ on Stack Overflow

How to create an array of classes and instance objects with it in Swift?

3 Answers 3

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related