Classes and Objects

Multiple Objects

The same class can create separate objects with separate values.

separate instances Two objects made from one class can produce different scalar results.

Multiple Objects

extra
multiple_objects.php
Replay: real traced execution (multi-file project)
<?php
class PackageBox
{
    public function __construct(public int $weight)
    {
    }
}

$extra = 2;
$firstWeight = (new PackageBox(3))->weight;
$secondWeight = (new PackageBox(4 + $extra))->weight;
$totalWeight = $firstWeight + $secondWeight;

echo "first=" . $firstWeight . "\n";
echo "second=" . $secondWeight . "\n";
echo "total=" . $totalWeight . "\n";

<?php
class PackageBox
{
    public function __construct(public int $weight)
    {
    }
}

$extra = 0;
$firstWeight = (new PackageBox(3))->weight;
$secondWeight = (new PackageBox(4 + $extra))->weight;
$totalWeight = $firstWeight + $secondWeight;

echo "first=" . $firstWeight . "\n";
echo "second=" . $secondWeight . "\n";
echo "total=" . $totalWeight . "\n";

<?php
class PackageBox
{
    public function __construct(public int $weight)
    {
    }
}

$extra = 5;
$firstWeight = (new PackageBox(3))->weight;
$secondWeight = (new PackageBox(4 + $extra))->weight;
$totalWeight = $firstWeight + $secondWeight;

echo "first=" . $firstWeight . "\n";
echo "second=" . $secondWeight . "\n";
echo "total=" . $totalWeight . "\n";

  1. $extra ← 2

    9$extra→ 2 = 2; //@extra=0, 510$firstWeight = (new PackageBox(3))->weight;

  2. public function __construct(public int $weight)

    pass 1 of 6
    3{4    public function __construct(public int $weight3)5    {6    }
    All 6 passes — pass 1 is the card above
    pass$weight
    13
    23
    33
    46
    56
    66

  3. $firstWeight = (new PackageBox(3))->weight;

    9$extra = 2; //@extra=0, 510$firstWeight = (new PackageBox(3))->weight3;11$secondWeight = (new PackageBox(4 + $extra))->weight;

  4. $firstWeight ← 3

    9$extra = 2; //@extra=0, 510$firstWeight→ 3 = (new PackageBox(3))->weight3;11$secondWeight = (new PackageBox(4 + $extra))->weight;

  5. $secondWeight = (new PackageBox(4 + $extra))->weight;

    10$firstWeight = (new PackageBox(3))->weight;11$secondWeight = (new PackageBox(4 + $extra))->weight6;12$totalWeight = $firstWeight + $secondWeight;

  6. $secondWeight ← 6, $totalWeight ← 9

    10$firstWeight = (new PackageBox(3))->weight;11$secondWeight→ 6 = (new PackageBox(4 + $extra))->weight6;12$totalWeight→ 9 = $firstWeight3 + $secondWeight6;1314echo "first=" . $firstWeight3 . "\n";15echo "second=" . $secondWeight6 . "\n";16echo "total=" . $totalWeight9 . "\n";
    outputfirst=3
second=6
total=9

  1. $extra ← 0

    9$extra→ 0 = 0;10$firstWeight = (new PackageBox(3))->weight;

  2. public function __construct(public int $weight)

    pass 1 of 6
    3{4    public function __construct(public int $weight3)5    {6    }
    All 6 passes — pass 1 is the card above
    pass$weight
    13
    23
    33
    44
    54
    64

  3. $firstWeight = (new PackageBox(3))->weight;

    9$extra = 0;10$firstWeight = (new PackageBox(3))->weight3;11$secondWeight = (new PackageBox(4 + $extra))->weight;

  4. $firstWeight ← 3

    9$extra = 0;10$firstWeight→ 3 = (new PackageBox(3))->weight3;11$secondWeight = (new PackageBox(4 + $extra))->weight;

  5. $secondWeight = (new PackageBox(4 + $extra))->weight;

    10$firstWeight = (new PackageBox(3))->weight;11$secondWeight = (new PackageBox(4 + $extra))->weight4;12$totalWeight = $firstWeight + $secondWeight;

  6. $secondWeight ← 4, $totalWeight ← 7

    10$firstWeight = (new PackageBox(3))->weight;11$secondWeight→ 4 = (new PackageBox(4 + $extra))->weight4;12$totalWeight→ 7 = $firstWeight3 + $secondWeight4;1314echo "first=" . $firstWeight3 . "\n";15echo "second=" . $secondWeight4 . "\n";16echo "total=" . $totalWeight7 . "\n";
    outputfirst=3
second=4
total=7

  1. $extra ← 5

    9$extra→ 5 = 5;10$firstWeight = (new PackageBox(3))->weight;

  2. public function __construct(public int $weight)

    pass 1 of 6
    3{4    public function __construct(public int $weight3)5    {6    }
    All 6 passes — pass 1 is the card above
    pass$weight
    13
    23
    33
    49
    59
    69

  3. $firstWeight = (new PackageBox(3))->weight;

    9$extra = 5;10$firstWeight = (new PackageBox(3))->weight3;11$secondWeight = (new PackageBox(4 + $extra))->weight;

  4. $firstWeight ← 3

    9$extra = 5;10$firstWeight→ 3 = (new PackageBox(3))->weight3;11$secondWeight = (new PackageBox(4 + $extra))->weight;

  5. $secondWeight = (new PackageBox(4 + $extra))->weight;

    10$firstWeight = (new PackageBox(3))->weight;11$secondWeight = (new PackageBox(4 + $extra))->weight9;12$totalWeight = $firstWeight + $secondWeight;

  6. $secondWeight ← 9, $totalWeight ← 12

    10$firstWeight = (new PackageBox(3))->weight;11$secondWeight→ 9 = (new PackageBox(4 + $extra))->weight9;12$totalWeight→ 12 = $firstWeight3 + $secondWeight9;1314echo "first=" . $firstWeight3 . "\n";15echo "second=" . $secondWeight9 . "\n";16echo "total=" . $totalWeight12 . "\n";
    outputfirst=3
second=9
total=12