Android Development with Kotlin

The notNull function

The notNull delegate is the simplest standard library delegate:

    var someProperty: SomeType by notNull()

The functions that provide most standard library delegates (including the notNull function) are defined in Delegates. To use them, we need to either refer to this object (Delegates.notNull()) or import it (import kotlin.properties.Delegates.notNull). We will assume in examples that this object has been imported, so we will omit a reference to it.

The notNull delegate allows us to define a variable as non-nullable, which is initialized at a later time and not during object construction. We can define a variable as non-nullable without providing a default value. This is an alternative to lateinit:

 lateinit var someProperty: ...