Kotlin for C# Developers

4.2. Objects

Kotlin doesn’t have static (or anything equivalent).

However, it has built-in support for singleton objects with the object keyword.

So the nearest equivalent to this…

C#

public static class Thing
{
    public static readonly string Name => "Bob"

    public static void DoStuff()
    {
        //...
    }
}

Thing.DoStuff();
Console.WriteLine(Thing.Name);

is this…

Kotlin

object Thing {
    const val name = "Bob"

    fun doStuff() {
        //...
    }
}

Thing.doStuff()
println(Thing.name)

Note: Objects are named in PascalCase, like classes and interfaces.

Objects can extend classes and implement interfaces.

Kotlin

object Thing : BaseClass(), Interface {
    override fun baseClassMethod() {
        //...
    }

    override fun InterfaceMethod() {
        //...
    }
}

Companion objects

The equivalent of a static method in a non-static class can be achieved with a companion object.

C#

public class Singleton
{
    public static Singleton Instance => new Singleton();

    private Singleton()
    {
        //...
    }

    public InstanceMethod()
    {
        //...
    }
}

var instance = Singleton.Instance;

instance.InstanceMethod();

Kotlin

class Singleton private constructor() {
    fun instanceMethod() {
        //...
    }

    companion object {
        val instance = Singleton()    // can access the private constructor
    }
}

var instance = Singleton.instance     // property called directly on the class

instance.instanceMethod()

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