Should Superman run in underwear to be faster?

Language Design
3

I’m not a chef in low-level language kitchen so i’d like to clarify it for myself. Please tell me where i’m wrong. (I’m not arguing, Just curious)

If we have that source code:

class Robin {
  val superman = Superman()
  fun letsRescueTheWorld() {
    superman.prepare { thing -> "<Super $thing />" }
  }
}

class Superman {
  inline fun prepare(putOn: (String) -> String): List<String> {
    return (underwear() + "Red cape with 'S'").map { putOn(it) }
  }
  private fun underwear(): List<String> {
    return listOf("Something", "that Superman would prefer", "not to show")
  }
}

Could the generated code be something like that ?:

class Robin {
  val superman = Superman()
  fun letsRescueTheWorld() {
    // inline transformation
    (superman.synthetic_underwear() + "Red cape with 'S'").map { thing -> "<Super $thing />" }
  }
}

class Superman {
  inline fun prepare(putOn: (String) -> String): List<String> {
    return (underwear() + "Red cape with 'S'").map { putOn(it) }
  }
  fun synthetic_underwear() = underwear()
  private fun underwear(): List<String> {
    return listOf("Something", "that Superman would prefer", "not to show")
  }
}

Than what is that “anything exposed by inline function that can break client code” ?

And if this assumption is in fact silly. let’s back to solutions suggested by you.
In particular by annotation do you mean something like Android @hide ?
And you did not mention are there any plans to implement any solution for that issue?