title: Set breakpoint on variable value change
body: <p>I'm just wondering if is it possible to set breakpoint on change of variable value (in any programming language and tool) ?</p>
  
  <p>For example, I want to say: "Stop anywhere, when value of variable 'a' will be changed".</p>
  
  <p>I know that there is ability to set condition breakpoint and to stop execution when a variable have some specific value, but I didn't hear about observing variable changes.</p>
  
  <p>If it is not possible, why ?</p>