Kotlin Brain Teasers

Discussion

All the speakers were added to both conference days. Why?

A data class’s copy function creates a shallow copy. Only one object is actually copied—the Event itself. For everything stored inside the object, the new Event just points at the same values as the old one.

Since both objects end up pointing at the same ArrayList object, any modifications to the list are visible in both.

Objects and References

When we created our first Event object, we didn’t supply a speakers value. Kotlin used the default from the class constructor, which creates a new ArrayList.

But for our second Event, we used copy, which doesn’t use the constructor defaults. Instead, for any property where you don’t supply a new value, copy takes the corresponding value ...