class C(x: R) NOT same as class C(private val x: R)

[SethTisue]

reported by @yanisIk at #568:

It says on the cheatsheet that
class C(x: R) is the same as class C(private val x: R) which is not true.
In this case (class C(x: R)), x is just a parameter that the constructor can receive and is only a local variable inside the constructor and not a member of the class.

there is discussion on that apparently abandoned PR about an appropriate fix