Classes and Objects

Object State

An object can update its own state across method calls.

state changes Method calls can update stored values, then return a scalar result that the page can display.

Object State

step
object_state.php
Replay: real traced execution (multi-file project)
<?php
class Counter
{
    public int $value = 0;

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

$step = 2;
$counter = new Counter();
$first = $counter->add($step);
$second = $counter->add(3);

echo "first=" . $first . "\n";
echo "second=" . $second . "\n";

<?php
class Counter
{
    public int $value = 0;

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

$step = 1;
$counter = new Counter();
$first = $counter->add($step);
$second = $counter->add(3);

echo "first=" . $first . "\n";
echo "second=" . $second . "\n";

<?php
class Counter
{
    public int $value = 0;

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

$step = 5;
$counter = new Counter();
$first = $counter->add($step);
$second = $counter->add(3);

echo "first=" . $first . "\n";
echo "second=" . $second . "\n";

  1. $step ← 2, $counter ← Counter

    13$step→ 2 = 2; //@step=1, 514$counter→ Counter = new Counter();15$first = $counterCounter->add($step2);16$second = $counter->add(3);

  2. $this->value ← 2

    pass 1 of 2
    6public function add(int $amount2): int7{8    $this->value→ 2 = $this->value + $amount2;9    return $this->value2;10}
    values this stepCounter$this

  3. $first ← 2

    14$counter = new Counter();15$first→ 2 = $counterCounter->add($step2);16$second = $counterCounter->add(3);

  4. $this->value ← 5

    pass 2 of 2
    6public function add(int $amount3): int7{8    $this->value→ 5 = $this->value + $amount3;9    return $this->value5;10}
    values this stepCounter$this

  5. $second ← 5

    15$first = $counter->add($step);16$second→ 5 = $counterCounter->add(3);1718echo "first=" . $first2 . "\n";19echo "second=" . $second5 . "\n";
    outputfirst=2
second=5

  1. $step ← 1, $counter ← Counter

    13$step→ 1 = 1;14$counter→ Counter = new Counter();15$first = $counterCounter->add($step1);16$second = $counter->add(3);

  2. $this->value ← 1

    pass 1 of 2
    6public function add(int $amount1): int7{8    $this->value→ 1 = $this->value + $amount1;9    return $this->value1;10}
    values this stepCounter$this

  3. $first ← 1

    14$counter = new Counter();15$first→ 1 = $counterCounter->add($step1);16$second = $counterCounter->add(3);

  4. $this->value ← 4

    pass 2 of 2
    6public function add(int $amount3): int7{8    $this->value→ 4 = $this->value + $amount3;9    return $this->value4;10}
    values this stepCounter$this

  5. $second ← 4

    15$first = $counter->add($step);16$second→ 4 = $counterCounter->add(3);1718echo "first=" . $first1 . "\n";19echo "second=" . $second4 . "\n";
    outputfirst=1
second=4

  1. $step ← 5, $counter ← Counter

    13$step→ 5 = 5;14$counter→ Counter = new Counter();15$first = $counterCounter->add($step5);16$second = $counter->add(3);

  2. $this->value ← 5

    pass 1 of 2
    6public function add(int $amount5): int7{8    $this->value→ 5 = $this->value + $amount5;9    return $this->value5;10}
    values this stepCounter$this

  3. $first ← 5

    14$counter = new Counter();15$first→ 5 = $counterCounter->add($step5);16$second = $counterCounter->add(3);

  4. $this->value ← 8

    pass 2 of 2
    6public function add(int $amount3): int7{8    $this->value→ 8 = $this->value + $amount3;9    return $this->value8;10}
    values this stepCounter$this

  5. $second ← 8

    15$first = $counter->add($step);16$second→ 8 = $counterCounter->add(3);1718echo "first=" . $first5 . "\n";19echo "second=" . $second8 . "\n";
    outputfirst=5
second=8