title: making dynamic defined constants php
body: <p>look at this syntax of variable name modifying:</p>
  
  <pre><code>${'a' . 'b'} = 'hello there';
  echo $ab;
  </code></pre>
  
  <p>this returns <code>"hello there"</code></p>
  
  <p>But i want do declare defined variables dynamical.</p>
  
  <pre><code>$error_code = $_GET[error_code]; //for example: 404
  define(E404, 'Not found');
  echo E{$error_code};
  </code></pre>
  
  <p>It return error, i want to generate <code>E404</code> dynamical on php codes and get its value.
  I have no idea what the syntax or the technique I'm looking for is here, which makes it hard to research. </p>