title: Scala Convert a string into a map
body: <p>What is the fastest way to convert this </p>
  
  <p><code>{"a":"ab","b":"cd","c":"cd","d":"de","e":"ef","f":"fg"}</code></p>
  
  <p>into mutable map in scala ? I read this input string from ~500MB file. That is the reason I'm concerned about speed. </p>