Visibility and Constructors

Private Property

A private property can only be changed from inside the class.

hidden state Private state lets the class control how a value changes.

Private Property

points
private_property.php
Replay: real traced execution (multi-file project)
<?php
class ScoreBox
{
    private int $score = 0;

    public function add(int $points): int
    {
        $this->score = $this->score + $points;
        return $this->score;
    }
}

$points = 7;
$box = new ScoreBox();
$total = $box->add($points);

echo "points=" . $points . "\n";
echo "total=" . $total . "\n";

<?php
class ScoreBox
{
    private int $score = 0;

    public function add(int $points): int
    {
        $this->score = $this->score + $points;
        return $this->score;
    }
}

$points = 3;
$box = new ScoreBox();
$total = $box->add($points);

echo "points=" . $points . "\n";
echo "total=" . $total . "\n";

<?php
class ScoreBox
{
    private int $score = 0;

    public function add(int $points): int
    {
        $this->score = $this->score + $points;
        return $this->score;
    }
}

$points = 12;
$box = new ScoreBox();
$total = $box->add($points);

echo "points=" . $points . "\n";
echo "total=" . $total . "\n";

  1. $points ← 7, $box ← ScoreBox

    13$points→ 7 = 7; //@points=3, 1214$box→ ScoreBox = new ScoreBox();15$total = $boxScoreBox->add($points7);

  2. $this->score ← 7

    6public function add(int $points7): int7{8    $this->score→ 7 = $this->score + $points7;9    return $this->score7;10}
    values this stepScoreBox$this

  3. $total ← 7

    14$box = new ScoreBox();15$total→ 7 = $boxScoreBox->add($points7);1617echo "points=" . $points7 . "\n";18echo "total=" . $total7 . "\n";
    outputpoints=7
total=7

  1. $points ← 3, $box ← ScoreBox

    13$points→ 3 = 3;14$box→ ScoreBox = new ScoreBox();15$total = $boxScoreBox->add($points3);

  2. $this->score ← 3

    6public function add(int $points3): int7{8    $this->score→ 3 = $this->score + $points3;9    return $this->score3;10}
    values this stepScoreBox$this

  3. $total ← 3

    14$box = new ScoreBox();15$total→ 3 = $boxScoreBox->add($points3);1617echo "points=" . $points3 . "\n";18echo "total=" . $total3 . "\n";
    outputpoints=3
total=3

  1. $points ← 12, $box ← ScoreBox

    13$points→ 12 = 12;14$box→ ScoreBox = new ScoreBox();15$total = $boxScoreBox->add($points12);

  2. $this->score ← 12

    6public function add(int $points12): int7{8    $this->score→ 12 = $this->score + $points12;9    return $this->score12;10}
    values this stepScoreBox$this

  3. $total ← 12

    14$box = new ScoreBox();15$total→ 12 = $boxScoreBox->add($points12);1617echo "points=" . $points12 . "\n";18echo "total=" . $total12 . "\n";
    outputpoints=12
total=12