Let’s go over what we learned in our exploration: I want my code to help me do the right thing.Īll in all, the in + contains combo becomes a nice little trick to improve readability and can be slightly safer if you are operating on a particular parameter because it gets automatically passed to your contains operator. Remember, our original goal was determinism. It’s just important to know that without a parameter you have no guarantee that all the conditions are operating on the same thing. I don’t mean to say this is a bad approach though. In fact, the last branch - isWednesday() - doesn’t really have anything to do with kittens or doggos at all. We could have accidentally used sound2 in one case and sound in another. You can’t actually be sure the sound parameter is used at all here. This is pretty powerful but could be an opportunity for mistakes. In this style, you can use anything that returns a Boolean on the left. In our previous examples, the in keyword was passing the parameter sound from the when expression to our custom type. Let’s start by looking at a basic example using ranges: var x = 5 when (x) One of the less-discussed features, however, is the ability for when to use the in operator. when can be returned, assigned, exhaustive, check types, smart cast, and much more. Quickly, however, folks tend to realize it can do a lot more. As an analog to Java’s switch statement, the when expression is a familiar way of branching logic with multiple conditions. Most programmers working in Kotlin are pretty familiar with the when expression. One of the tools in Kotlin that allows us to achieve greater determinism is the language’s when expression. And I really like sealed classes for representing state. I like using types for expressiveness and safety. It’s part of why I love Kotlin as a programming language.

Kotlin internal fun