title: How to use range.map in swift 3/4?
body: <p>I have the code below, which works in swift 2.3. I am struggling to understand how to convert it to swift 3/4 - the issue it those is 
  <code>Value of type 'Range&lt;Int&gt;' has no member 'map'</code>      </p>
  
  <pre><code>let grainSize = CGFloat(0.01)
          let min = CGFloat(-3)
          let max = CGFloat(3)
          let range = Range&lt;Int&gt;(uncheckedBounds: (lower: Int(min/grainSize), upper: Int(max/grainSize)))
          let lol = NSRange(range)
  
          var points = range.map { step -&gt; CGPoint in
              let i = grainSize * CGFloat(step)
              let x = x_base + (i * controller.width / 4.0)
              let y = y_base + (m * equation(i))
              if x_init == CGFloat.max { x_init = x }
              return CGPointMake(x, y)
          }
          points.append(CGPointMake(x_init, y_base))
          points.forEach { renderer.lineTo($0) }
  </code></pre>
  
  <p>I am wondering if someone can point me in the right direction for this - even to documentation regarding this, as I can't find anything about it in apple docs either =[</p>