// import StringInterpolationTest._
object Test extends App {
  import StringInterpolationTest._
  val x = 1
  val s = cap"boo $x"
  println(s)
}
object StringInterpolationTest {
  implicit class X(val sc: StringContext) extends AnyVal {
    def cap(args: Any*) = ???
  }
}

When the import is outside the object definition, it cannot find the implicit class containing a method cap. However this code does compile.

Scala IDE version:
        4.3.0.v-2_11-201512011536-499c89a
Scala compiler version:
        2.11.7
Scala library version:
        2.11.7
Eclipse version:
        4.4.2.v20150204-1700
Class loader store: 1 entries
        Compiler v. 2.11.7(/Applications/eclipse/plugins/org.scala-lang.scala-compiler_2.11.7.v20150622-112736-1fbce4612c.jar)