Singleton abstract class in Kotlin

I am implementing a library following a template method design pattern. It involves creating costly IO connection. To avoid any resource leaks, i want to enforce singleton instance on abstract class level. client just need to override the method which involves logic.

how can i do with kotlin?

abstract class SingletonConnection{
     fun start(){ /* code */ }
     fun connect(){ /* code */ }
     abstract fun clientLogic()   
}

If class A extends this, it should be singleton class. not allowed to initialise multiple times. how to do in kotlin?

Unfortunately, there is no way to enforce that only objects (singletons in Kotlin) can inherit from a certain abstract/open class or interface in Kotlin. object declaration is just syntactic sugar for a regular class with a Singleton pattern.

I know it's not much, but I guess you can achieve this to a certain degree by adding documentation, asking users to implement this class by Singletons alone.

By the way, I would use an interface instead of an abstract class for this purpose.