title: Why plus operator between two shorts returns an Int
body: <p>I'm working on a program which run on machines with limited resources. I must optimize as much as I can the memory usage.</p>
  <p>To do so, I set Short type in parameter of different functions, but then, I noticed at one point that my variables which are Short, give an Int when I use the '+' operator.</p>
  <p><strong>From Primitive.kt:</strong>
  <code>public operator fun plus(other: Short): Int</code></p>
  <p>Why does it return an Int rather than a short ?</p>
  <p>Does the JVM optimize the code behind the scene ?</p>
  <p>If i use massively the toShort function, will this slow my code ?</p>