hashmap datastructure with php REPL

php > $user_cache=array("uid1"  => "1", "uid2" => "2");

php > echo $user_cache["uid1"];
1

php > if(!$user_cache["uid3"]) { echo "cache miss";}
PHP Notice:  Undefined index: uid3 in php shell code on line 1

Notice: Undefined index: uid3 in php shell code on line 1
cache miss