Chain.playground.swift

//: Playground - noun: a place where people can play

import Foundation

//: We have to define init() method for ObjectType() to work

protocol Creatable {
    init()
}

class Base: Creatable {
    required init() {}
}

//: Bunch of dummies

class A:Base {}
class B:Base {}
class C:Base {}
class D:Base {}
class E:Base {}
class F:Base {}

//: Base chain that holds some object

class BaseChain<ObjectType:Creatable> {

    var object: ObjectType

    init() {
        object = ObjectType()
    }
    
    func printSelf() -> Self {
        print("Object.class = \(object.dynamicType); Chain.dynamicType = \(self.dynamicType)")
        return self
    }
}

//: Chain LEVEL 1 class

class Chain<ObjectType:Creatable> : BaseChain<ObjectType> {
    
    func chain<DynamicType: Creatable>(type: DynamicType.Type) -> Subchain<DynamicType, Chain<ObjectType>> {
        return Subchain<DynamicType, Chain<ObjectType>>(parent: self)
    }
}

//: Chain LEVEL 1+

class Subchain<ObjectType:Creatable, ParentObjectType> : BaseChain<ObjectType> {

    var parent: ParentObjectType
    
    init(parent parent_: ParentObjectType) {
        parent = parent_
        super.init()
    }
    
    func chain<DynamicType: Creatable>(type: DynamicType.Type) -> Subchain<DynamicType, Subchain<ObjectType, ParentObjectType>> {
        return Subchain<DynamicType, Subchain<ObjectType, ParentObjectType>>(parent: self)
    }
    
    func end() -> ParentObjectType {
        return parent
    }
    
}

/*: 

Do some chained calls.

.end() allows to get back to parent chain

*/

Chain<A>()
    .chain(B.self)
        .chain(C.self)
            .chain(D.self)
                .chain(E.self)
                    .chain(F.self)
                        .printSelf()
                    .end()
                .printSelf()
                .end()
            .printSelf()
            .end()
        .printSelf()
        .end()
    .printSelf()
    .end()
.printSelf()