Android Development with Kotlin

Property delegation to the Map type

The standard library contains extensions for Map and MutableMap with the String key type that provides the getValue and setValue functions. Thanks to them, map can also be used as a property delegate:

    class User(map: Map<String, Any>) { // 1 
        val name: String by map 
        val kotlinProgrammer: Boolean by map 
    } 
 
    // Usage 
    val map: Map<String, Any> = mapOf( // 2 
        "name" to "Marcin", 
        "kotlinProgrammer" to true 
    ) 
    val user = User(map) // 3 
    println(user.name)  // Prints: Marcin 
    println(user.kotlinProgrammer)  // Prints: true 

1. The map key type needs to be String, while the value type is not restricted. It is often Any or Any?.
2. This creates Map, which contains all the values.
3. Provides a map to an object.

This can be useful ...