: run { // execute this block if null } But this seems not to be quite as readable as a simple if-else statement. [kotlin] assertEquals(listOf(2, 4, 6, 8), listWithNull mapNotNull { it * 2 }) [/kotlin] 18.4 Elements operations contains. A quick and practical guide to collection processing in Kotlin. Kotlin is a modern programming language that compiles to Java bytecode.It is free and open source, and promises to make coding for Android even more fun. Download ☔ WhatIf has been downloaded in more than 50k Kotlin and Android projects all over the world! internal. Kotlin™ is protected under the Kotlin Foundation and licensed under the Apache 2 license. I have declared below variables: val occupations = mapOf(Pair("Malcolm", "Captain"), Pair("Kaylee", "Mechanic")) val InlineOnly: public inline fun < T > Collection. 3. Supported and developed by JetBrains Supported and developed by JetBrains Here, you added safe call operators. Also, you might find this Q&A useful: In Kotlin, what is the idiomatic way to deal with nullable values, referencing or converting them In a way, the double exclamation mark is Kotlin yelling at you not to use it too often!! How can i declare an empty collection for mapOf,listOf and setOf in Kotlin? Add a dependency code to your module's build.gradle file. isNotEmpty (): Boolean = !isEmpty() /* * * Returns `true` if this nullable collection is either null or empty. dropWhile is another filter that takes a predicate but dropWhile works from index 0 -> n and dropLastWhile works from index n -> 0. In general, one should strive to use read-only lists, however, mutability is still often useful at construction time, especially when dealing with third-party libraries with non-functional interfaces. * Returns `true` if the collection is not empty. The method stops removing elements as soon as an element does not meet the condition of the predicate. Returns true if the element is found in the collection. * @sample samples.collections.Collections.Collections.collectionIsNotEmpty */ @kotlin. All these code examples which use "docSnapshot.exists" checking, arent they forgetting that this is not a transaction, so it can not guarantee that by the time the client find out that doc does not exist and it triggers a create new doc, someone else might have created that doc, in … ... As we can see, if we omit the prefix and suffix, they are the empty string, and if we omit the separator, then it is the string “, “. WhatIf ☔ Fluent expressions of Kotlin for handling single if-else statements, nullable, collections, and boolean. If we try to drop more elements than the collection contains, we’ll just be left with an empty List. Returns a list containing the non-null results of applying the given transform function to each element of the original collection. 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