Delegation in Kotlin: A Beginner’s Guide to Code Modularity and Reusability
Delegation is a programming technique that allows one object or class to delegate some of its responsibilities to another object or class. In Kotlin, you can use delegation to create reusable and modular code, and to avoid inheritance hierarchies.
To use delegation in Kotlin, you can use the by
keyword to specify a delegate object. For example, consider the following interface and class:
interface Base {
fun foo()
}
class Derived(b: Base) : Base by b
The Base
interface defines a single method, foo
, and the Derived
class implements Base
by delegating to an instance of Base
. This means that the Derived
class does not have to implement the foo
method itself; it can simply delegate the call to the delegate object.
Here is an example of how you might use the Derived
class:
fun main() {
val base = object : Base {
override fun foo() {
println("foo called on base object")
}
}
val derived = Derived(base)
derived.foo()
}
In this example, the main function creates an instance of the Base
interface and passes it to the constructor of Derived
. When the foo
method is called on the derived
object, it is delegated to the base
object, which prints "foo called on base object" to the console.
You can also use delegation to create classes that have multiple behaviors or interfaces. For example, consider the following interface and class:
interface Base1 {
fun foo()
}
interface Base2 {
fun bar()
}
class Derived(b1: Base1, b2: Base2) : Base1 by b1, Base2 by b2
The Derived
class implements both the Base1
and Base2
interfaces by delegating to separate delegate objects. This allows the Derived
class to have multiple behaviors or interfaces, without having to implement them itself.
Overall, delegation is a powerful technique in Kotlin that allows you to create reusable and modular code, and to avoid inheritance hierarchies. It is a useful tool for organizing and extending your codebase in a flexible and scalable way.