title: Groovy: on the fly properties
body: <p>In Javascript you can define an object with properties a and b like so:</p>
  
  <pre><code>myObj={a:'a',b:'b'}
  </code></pre>
  
  <p>and then you can add a property c like so </p>
  
  <pre><code>myObj.c = 'c'
  </code></pre>
  
  <p>whats the equivalent of that in Groovy? Do I have to use metaClass? </p>
  
  <p>Use case: JSON converters in Grails do not add transient properties to the response, i would like to just attach a random property to each element of my object list. </p>