Solved Add or remove a string from a variable

Hello,
How do I add/remove a string to/from a variable?
For example, when a player joins a certain world, I want to be able to add their name to $players
Like this:

PHP:

$player = $event->getPlayer()->getName();
$players = $players + $player; //How do I do this with strings


Then when the player leaves:

PHP:

$player = $event->getPlayer()->getName();
$players = $players - $player; //Again, Strings?


Thanks.

Code:

public $players = [];
-------
//when player joins:
$this->players[$event->getPlayer()->getName()] = $event->getPlayer()->getName();
//when player leaves
if(isset($this->players[$event->getPlayer()->getName()])){
unset($this->players[$event->getPlayer()->getName()]);
}
//get all player names stored
foreach(array_keys($this->players) as $player){
echo $player;
}
//get specific player
if(isset($this->players[$event->getPlayer()->getName()])){
echo "player exists";
}else{
echo "player not found";
}

anyways, why wont you use $this->getServer()->getOnlinePlayers(); ?

Thank you very much!!!
Because I need the players in the match, the world or the server.

well if thats the case, just add strtolower() on names to make sure its equivalent to the player inside the session.

Prevent holding player instances to reduce the chance of memory leak.

How do I do that?

I ask you not to do that

Well how do I no hold them?

Then how do you hold them at all?

Ok now I am really confused.