title: How to instantiate class and init from string in Swift?
body: <p>I could instantiate class from string in ObjC.For example,I have defined new DBCell class through subclassing UITableViewCell,and I instantiate class from name with these codes:</p>
  
  <pre><code> DBCell *cell=[tableView dequeueReusableCellWithIdentifier:cellClassname];
      if (cell==nil) {
          Class cellClass=NSClassFromString(cellClassname);
          cell=[cellClass alloc];
          cell=[cell initWithStyle:cellStyle reuseIdentifier:cellClassname];
      }
  </code></pre>
  
  <p>Now I need migrate codes to Swift,I have redefined DBCell class in Swift:</p>
  
  <pre><code> class DBCell: UITableViewCell {
      var label:String?
      var key:String?
      var managedObject:NSManagedObject?
      var delegate:AnyObject?
      convenience override init(style: UITableViewCellStyle, reuseIdentifier: String!) {
          self.init(style: style, reuseIdentifier: reuseIdentifier)
          self.textLabel.font=UIFont.preferredFontForTextStyle(UIFontTextStyleCaption1)
          self.backgroundColor=UIColor.blackColor()
          self.textLabel.backgroundColor=UIColor.blackColor()
      }
      }
  </code></pre>
  
  <p>But how can I instantiate class and invoke the appropriate init function? </p>