object expression in Kotlin

Object expression is a structure that creates a single instance of an object:
```
val coords = object {
    var x = 10
    var y = 10
}
```
It is often used as a substitution to a Java anonymous class:
```
window.addMouseListener(object : MouseAdapter() {
    override fun mouseClicked(e: MouseEvent) { /* ...*/ }
    override fun mouseEntered(e: MouseEvent) { /* ...*/ } 
})
```