title: Apply a directive conditionally
body: <p>I am using Material 2 to add <code>md-raised-button</code>. I want to apply this directive only if certain condition becomes true.</p>
  
  <p>For example: </p>
  
  <pre><code>&lt;button md-raised-button="true"&gt;&lt;/button&gt;
  </code></pre>
  
  <p>Another example:
  I created a basic dynamic reactive form in plunker.
  I am using <code>formArrayName</code> directive of reactive form for array of controls.
  I want to apply <code>formArrayName</code> directive only if specific condition becomes true, otherwise don't add <code>formArrayName</code> directive.</p>
  
  <p>Here is a <a href="https://plnkr.co/edit/oPZ7PyBSf8jjYa2KVh4J?p=preview" rel="noreferrer">plunker link</a>.</p>