Why isn't this a valid contract? It says "Only references to parameters are allowed in a contract description". What does that mean?

It means, you can't reference a property (

value

in this case) in a contract. Only parameters of the method (but yours doesn't have any). Like this maybe? (untested)

@ExperimentalContracts
fun isValidEmail(value: String?): Boolean {
	contract {
		returns(true) implies (value != null)
	}
	return value != null && mailRegex.matches(value)
}

Ah damn, this whould have been to good

Hm. I just tried it with one indirection, but the compiler doesn't check it two levels deep 🙍‍♂️ :

hmm, but this is an inline class .. . doesn't that mean

value

is

this

?!?