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Mastering Kotlin Essentials

Maps

Explore how to work with maps in Kotlin collections to manage key-value associations. Understand how to create, retrieve, add, and remove entries in maps while utilizing generics for flexible types.

We'll cover the following...

Key-value mapping

We use maps to keep associations from keys to their values. For instance:

  • From user ID to an object representing the user

  • From a website to its IP address

  • From a configuration name to data stored in this configuration

Kotlin 1.5
class CachedApiArticleRepository(
    val articleApi: ArticleApi
) {
    val articleCache: MutableMap<String, String> =
        mutableMapOf()
    fun getContent(key: String) =
        articleCache.getOrPut(key) {
            articleApi.fetchContent(key)
        }
}
class DeliveryMethodsConfiguration(
    val deliveryMethods: Map<String, DeliveryMethod>
)
class TokenRepository {
    private var tokenToUser: Map<String, User> = mapOf()
    fun getUser(token: String) = tokenToUser[token]
    fun addToken(token: String, user: User) {
        tokenToUser[token] = user
    }
}

Creating maps

We can create a map using the mapOf function and then use key-value pairs as arguments to specify key-value associations. ...