[swift-users] Store objects of generic types in a data structure

Hugo Lundin hugo at hugolundin.se
Sat Apr 8 07:22:13 CDT 2017

Dear all, 

I am currently playing with a concept in Swift to store statistics in apps using generic types. One of the key parts are the ability to register properties (for example booleans, strings and integers - but also more complex data types such as dates):

stats.add(description: "iOS Version", property: {
   return UIDevice.current.systemVersion as? String

stats.add(description: "HealthKit authorized", property: {
   return HealthKit.authorized

I've played with different kind of implementations of this, but feel that Swift limits me in some ways, because I can not find a way to store different types in a list. 

I have tried to implement it in Java, and this works: 

import java.util.ArrayList;
import java.util.List;
public class Property<T> {
    private String description;
    private T property;

    public Property(String description, T property){
        this.description = description;
        this.property    = property;

    public String getDescription() {
        return description;

    public T getProperty() {
        return property;

public class Analytics {
    private List<Property> properties = new ArrayList<>();

    public Analytics() {


    public static void main(String[] args) {
        Analytics stats = new Analytics();
        stats.add(new Property("HealthKit", false));
        stats.add(new Property("iOS Version", "9.3"));

    public void add(Property property) {

    public void show() {
        for (Property p : properties) {
            System.out.println(p.getDescription() + ": " + p.getProperty());

How would I be able to achieve this in Swift? My current idea of this approach does not seem to work, but also the idea to create specific subclasses for every type (and then type cast the different properties), gives a lot of work, and there would be a limitation for which types are available. 

Thank you for your time. 

Hugo Lundin. 

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