Just for kicks, I decided to try this in Java 8 to see the difference. In this case, I wanted to sort by the number of orders my hypothetical customer placed, so I used it.orders.size. Help is never far away consult extensive community resources or ask the Kotlin team directly. Enjoy the benefits of a rich ecosystem with a wide range of community libraries. As a matter of fact, it’s only one line of code.įun Shop.getCustomersSortedByNumberOfOrders(): List. Kotlin has great support and many contributors in its fast-growing global community. As usual with Kotlin, this wasn’t a very difficult problem. Cool.This portion of the Kotlin Koans tutorial deals with sorting a collection functionally. So… err… that's a long way of saying 'nope'. I checked what happens if I tried to use that sealed interface in a different package: In some sense, sealed classes are similar to enum classes: the set of values for an enum type is also restricted, but each enum constant exists only as a single instance, whereas a subclass of a sealed class can have multiple instances, each with its own state. The docs say this, which makes a kind of sense: If it wasn't a sealed interface, then anything else could implement it, so I'd either need to handle that here, or have an else. The compiler knows that the only two possible options for a SomeSealedInterface are one of either a SomeSealedImplementation or a SomeOtherSealedImplementation: there can be no other options.

The key bit here is not so much what I'm testing, it's that the when expression doesn't need an else option. Val result = handleSomeSealedInterfaceInstance(testObj) Val testObj = SomeSealedImplementation('some property value')

In Kotlin a todo is not just a marker of guilt and a pretence one will come back and finish things later, but an actual function: of the TODO function')Ĭlass TodoTest `It should throw a NotImplementedError`() My mindset was 'OK, I need to do to make the koans exercise pass, but what is that all about?' And today I shall continue. I used the koans as a jumping off point to look at stuff. Kotlin: the next morning learning Kotlin stuff.Kotlin: an afternoon learning Kotlin stuff.I started doing the Kotlin koans a while back, and discuss my meagre progress in these articles:

Kotlinkoans