title: scala type conversion using implicit -> enforce type checks
body: <p>Here is simple bit of code and question related.</p>
  
  <p>Is there a way to tell scala compiler that if type to which this conversion will be applied to not exists than error on compilation time!</p>
  
  <p>I can see a warning in the sbt tool but can't see any description so war.</p>
  
  <pre><code>class A(val n: Int) {
      def +(other: A) = new A(n + other.n)
  }
  
  object A {
      implicit def fromMyInt(n: Int) = new A(n)
  }
  
  val r = 1 + new A(1)
  
  println( r )
  </code></pre>