title: How can I format string with fixed length in swift
body: <p>For example:
  var str = String(format: "%12s - %s", "key", "value")</p>
  
  <p>What I want is key will hold chars of length of 12.
  key__________ - value</p>
  
  <p>(underscore here is whitespace)</p>
  
  <p>Thanks.</p>