For people who have difficulties with constants and opcache_reset().
If you include a file with constant and do an opcache_reset() in the same file, you'll probably have some error like :
"Notice: Constant already defined"
The trick is to call opcache_reset() in an isolated file, then include another file that include the file with constants.
With this trick, the opcache will be reset in a.php and when b.php will be included, the constants will not be in cache anymore.