The same key can’t appear twice in a map, but different keys may point to the same value. 24.6 Getting information from the systemĪ map is an unordered collection of pairs, where each pair is comprised of a key and a value.Īs shown in the diagram above, keys are unique.22.6 Delegated properties as conventions.21.3 First-class and higher-order functions.20.5 Difference between Java and Kotlin exceptions.19.5 “Static” values and functions from Kotlin.19.3 Making your Kotlin Code Java-friendly.Section IV: Intermediate Topics Section 4: 9 chapters Show chapters Hide chapters 18.6 Generic type variance (a.k.a., in and out declarations).18.3 Creating your own generic constraints.18.2 Extension functions on types with generic constraints.18.1 Anatomy of standard library generic types. 17.4 Interfaces in the standard library.16.2 Enum class properties and functions.11.3 Understanding state and side effects. Section III: Building Your Own Types Section 3: 8 chapters Show chapters Hide chapters Little did we realize, actually this approach is also used to destructure the key-value of map entries.Section I: Kotlin Basics Section 1: 7 chapters Show chapters Hide chapters Well, it seems pretty limited, and we’re not likely to use it to destructure a list or array. The bracket approach although concise, it doesn’t handle nullable collection. It also compile error val listFirstItem = list? // list: List? = listOf(1) val arrayFirstItem = array? // array: Array? = arrayOf(1) val mapWithKey0 = map? // map: Map? = mapOf(0 to 1) 2. val listFirstItem = list // list: List? = listOf(1) val arrayFirstItem = array // array: Array? = arrayOf(1) val mapWithKey0 = map // map: Map? = mapOf(0 to 1) // Neither can we do below. However, it cannot be used for Sequence // Compile Error! val sequenceFirstElement = sequence // sequence = sequenceOf(1)īesides, it can’t be used for nullable list, array, or map // Compile error, as all of them are nullable. val listFirstItem = list // list = listOf(1) val arrayFirstItem = array // array = arrayOf(1) val mapWithKey0 = map // map = mapOf(0 to 1) It can be used for the list, array, and map. This is the default recommended approach. There are 4 approach?! What’s their differences? 1. How do you do it? Which one do you use below? If you’ve had to use Kotlin Collection, you probably have access to its element before.
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