Swift Class Cluster demo

ClassCluster.swift

public class Pokemon {
    private init() {}
    public var name: String { fatalError() }
}

private class Pikachu: Pokemon {
    override var name: String { return "ピカチュウ" }
}

private class Snorlax: Pokemon {
    override var name: String { return "カビゴン" }
}

extension Pokemon: _Cluster {
    public convenience init?(_ arg: String) {
        self.init {
            switch arg {
            case "pika": return Pikachu()
            case "snor": return Snorlax()
            default: return nil
            }
        }
    }
}

private protocol _Cluster {}
extension _Cluster {
    init?(@noescape _cluster: () -> Self?) {
        guard let _self = _cluster() else { return nil }
        self = _self
    }
}

main.swift

Pokemon("pika")?.name // -> "ピカチュウ"
Pokemon("snor")?.name // -> "カビゴン"
Pokemon("bang")?.name // -> nil