Array returns NULL in class

Question

I'm trying to declare a global array but when trying to retrieve it it returns NULL

GamesManager.php

namespace TMSE;

use PDO;


class GamesManager extends Main {

protected $DB;

public $cards = array();

public function __construct() {
    global $cards;
     $this->$cards = array('2' => 2, '3' => 3, '4' => 4, '5' => 5, '6' => 6, '7' => 7, '8' => 8, '9' => 9, 'T' => 10, 'J' => 10, 'Q' => 10, 'K' => 10, 'A' => 11);
     var_dump($cards);
}


public function pullCard() {
    global $cards;
    var_dump($cards);
}
}

Both var_dumps return NULL

Ro Achterberg · Accepted Answer · 2020-12-20 18:59:50Z

You seem to be a little confused about variable scope. There's also an errant $ in $this->$cards. While this is valid syntax, it's not doing what you expect.

Consider the following to get an idea of what's going wrong with your code. See comments and output at the end for explanation.

<?php

$cards = [4, 5, 6]; // Global scope

class GamesManager
{
    public $cards = []; // Class scope
    
    public function __construct()
    {
        $this->cards = [1, 2, 3]; // This will set the class variable $cards to [1, 2, 3];
        
        var_dump($this->cards); // This will print the variable we've just set.
    }
    
    public function pullCard()
    {
        global $cards; // This refers to $cards defined at the top ([4, 5, 6]);
        
        var_dump($this->cards); // This refers to the class variable named $cards
        /*   
        array(3) {
          [0]=>
          int(1)
          [1]=>
          int(2)
          [2]=>
          int(3)
        }
        */
        
        var_dump($cards); // This refers to the $cards 'imported' by the global statement at the top of this method.
        /*
        array(3) {
          [0]=>
          int(4)
          [1]=>
          int(5)
          [2]=>
          int(6)
        }
        */
    }
}

$gm = new GamesManager;
$gm->pullCard();
/*
array(3) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  int(3)
}
array(3) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  int(3)
}
array(3) {
  [0]=>
  int(4)
  [1]=>
  int(5)
  [2]=>
  int(6)
}
*/

Mikhail Prosalov · Accepted Answer · 2020-12-20 18:59:21Z

0

In this case you don't need a 'global' keyword. Just access your class attributes using $this keyword.

class GamesManager extends Main {

    protected $DB;

    public $cards = array();

    public function __construct() {
        $this->cards = array('2' => 2, '3' => 3, '4' => 4, '5' => 5, '6' => 6, '7' => 7, '8' => 8, '9' => 9, 'T' => 10, 'J' => 10, 'Q' => 10, 'K' => 10, 'A' => 11);
        var_dump($this->cards);
    }


    public function pullCard() {
        var_dump($this->cards);
    }
}

answered Dec 20, 2020 at 18:59

Mikhail Prosalov

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