Making the world a little more type-safe 🌍🏆

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Reduce the need for emptiness checks and reduce unsafe APIs with NonEmptyCollections.

You can use NonEmptyList, NonEmptySet and NonEmptyMap to restrict the input of functions to make your code safer and avoid unnecessary runtime exceptions.

For a detailed explanation see our related article Non-Empty Lists in Kotlin.

This is an early version and work in progress. Do not hesitate to give feedback, ideas or improvements via an issue.


Average without exceptions

With the NonEmptyList type, we can make sure that at least one element is always a list. If we want to calculate the average of that list, it is impossible to compile a program where an invalid input is passed to our function.

fun NonEmptyList<Int>.average() = sum() / size
nonEmptyListOf<Int>().average()   // This does not compile! ❌

nonEmptyListOf(1, 2, 3).average() // This does! ✅

Non-empty Shopping-Cart

Let's imagine an online shop, where you can put articles into a shopping cart. If you have some articles in the shopping cart, you should be able to share the articles with your friends, save them for later on a wish list or directly buy them. But these three features just make sense if the shopping cart is not empty. Wouldn't it be cool to already prevent at compile-time that somebody tries these features with an empty set of articles?

sealed class ShoppingCart {
    object Empty : ShoppingCart()

    data class Filled(
        val articles: NonEmptySet<Article>
    ) : ShoppingCart() {

        fun buy(paymentType: PaymentType) =
        fun share() = articles.share()
        fun saveTo(wishList: WishList) = articles.saveTo(wishList)

fun NonEmptyCollection<Article>.buy(paymentType: PaymentType) { 💸 }

fun NonEmptyCollection<Article>.share() { 💬 }

fun NonEmptyCollection<Article>.saveTo(wishList: WishList) { 💾 }

The devs, who implement buy, share and saveTo don't have to handle the empty case. The consumers of these APIs don't have to think of exception handling, because they are forced by the compiler to provide a valid input. We would say, that's a win-win situation 🏆.

🏃 Library Setup

1. Add the repository


allprojects {
    repositories {
        maven { url = uri("") }

2. Add the dependency


dependencies {

👤 Author

This Kotlin library is created with ❤️ by QuickBird Studios.

❤️ Contributing

Open an issue if you need help, if you found a bug, or if you want to discuss a feature request.

Open a PR if you want to make changes to NonEmptyCollections.

📃 License

NonEmptyCollections is released under an MIT license. See License for more information.


A type-safe implementation for collections that cannot be empty. Life is too short for emptiness-checks!

Nonemptycollections Info

⭐ Stars 44
🔗 Source Code
🕒 Last Update a month ago
🕒 Created 10 months ago
ğŸž Open Issues 2
➗ Star-Issue Ratio 22
ğŸ˜Ž Author quickbirdstudios