Dfyjkt

I define a class field as array constant.
Then I try to use that array field values as an index in another array:

class A

 const NAMES = Array(
 "A",
 );

 static function run()
 
 $arr = array("A"=>"123");


 $arNames = constant('self::NAMES');

 foreach ($arNames as $name) 
 echo '$name=' . $name . '<BR>';
 echo '$arr[$name]=' . $arr[$name] . '<BR>';
 

 $name2=$arNames[0];
 echo '<BR>'.'$name2=' . $name2 . '<BR>';
 echo '$arr[$name2]=' . $arr[$name2] . '<BR>';
 


A::run();

On one server under PHP 7.1.23 it works fine and output is :

$name=A
$arr[$name]=123

$name2=A
$arr[$name2]=123

But it works wrong on another server whith the same PHP, libs and so on. It sets the $arr[$name] to the NULL in the foreach loop. But the direct request by numeric index also works fine:

$name=A
$arr[$name]=

$name2=A
$arr[$name2]=123

Is there any restriction for using constant arrays?
I didn't find anything on http://php.net/manual/ru/language.constants.syntax.php or elsewere.

Addition
Now I find out the difference between severs. If opcode is enabled, the loop blok works wrong.