make your implicit classes `val` parameters `private`

implicit.scala

Welcome to Scala version 2.11.7 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_66).

scala> implicit class Foo(val x: Int) { def foo = x * 2 }
defined class Foo

scala> 3.x
res0: Int = 3

scala> :reset
Resetting interpreter state.
Forgetting defined types: Foo

scala> implicit class Foo(private val x: Int) { def foo = x * 2 }
defined class Foo

scala> 3.x
<console>:12: error: value x is not a member of Int
       3.x
         ^