Set.equals

@ExperimentalContracts
fun foo(bar: Int) {
    contract { 
        returns() implies (bar < 10)
    }
}

<

implies (bar < 10)

fun test() {
        val x = Foo(11)
        require(x.x > 10)
        
        if (x.x == 3) {
            //Compile error because x must be > 10
        }
    }

even though implies takes a Boolean argument, actually only a subset of valid Kotlin expressions is accepted: namely, null-checks (

== null

,

!= null

), instance-checks (

is

,

!is

), logic operators (

&&

,

||

,

!

)

ìf (x < 0) throw Exception()

During an instance initialization, the initializer blocks are executed in the same order as they appear in the class body, interleaved with the property initializers:

Nothing

listOf<Nothing>()

Array<Nothing>

Nothing[]

Any?