scala> extension (s: String)(using z: Int) { def f(i: Int) = s*(i*z); def g_:(i: Int) = (s*(i*z)).reverse }
def f(s: String)(using z: Int)(i: Int): String
def g_:(i: Int)(s: String)(using z: Int): String

scala> "xyz" f 5
-- [E008] Not Found Error: -----------------------------------------------------
1 |"xyz" f 5
  |^^^^^^^
  |value f is not a member of String.
  |An extension method was tried, but could not be fully constructed:
  |
  |    f("xyz")(/* missing */summon[Int])
  |
  |    failed with:
  |
  |        No given instance of type Int was found for parameter z of method f
1 error found

scala> "xyz" g_:  5
-- [E172] Type Error: ----------------------------------------------------------
1 |"xyz" g_:  5
  |            ^
  |     No given instance of type Int was found for parameter z of method g_:
1 error found

scala> ("xyz" g_: 5)(using 2)
val res10: String = zyxzyxzyxzyxzyxzyxzyxzyxzyxzyx