Hi Sviatoslav Melnychenko. This is a kotlin’s Delegation Pattern. With that you can easily decorate things (so for me this thing actually helps to implement Decorator pattern):

interface Sample {
    fun method1()
    fun method2(arg: String)
    fun method3(): String
    fun method4()
}

class Implementation : Sample {
    //...
}

class Decorator(sample: Sample) : Sample by sample {
    //...now you able to implement not all 4 methods,
    //but only those, you needed
}