<p>I have the following code and when I define a variable in the constructor I get the error "PHP Fatal Error: Constant expression contains an invalid operation". It works fine when used in Laravel framework. </p> <pre class="brush:php;toolbar:false;"><?php namespace App; class Amazon { protected $serviceURL = config('api.amazon.service_url'); public function __construct() { } }</pre> <p>I saw this question: PHP error: fatal error: constant expression contains an invalid operation But my code doesn't declare any static content, so this answer doesn't solve my problem. </p>

<?php

namespace App;

class Amazon
{
  protected $serviceURL;

  public function __construct()
  {
    $this->serviceURL = config('api.amazon.service_url');
  }
}