Question

Change a value inside foreach don't have any effect,

$data = array(
    'key' => array(
        'key1' => 'value1'
    )
);

foreach($data as $key => $obj) {
    $obj['key2'] = 'value2';
}

$data['key']['key2'] == 'value2'; // false

while

$data = array(
    'key' => array(
        'key1' => 'value1'
    )
);

foreach($data as $key => $obj) {
    $data['key'] == $obj; // true
    $data['key']['key2'] = 'value2';
}

$data['key']['key2'] == 'value2'; true

Solution

By default, PHP array assignment by value rather than reference

$a = array('1', '2');
$b = $a;

$a[0] = '11';
echo $b[0]; // still '1'

And, array comparation also done by value comparation

$a = array('1', '2');
$b = array('1', '2');

echo $a == $b; // true

We can using & to passing by reference,

$a = array('1', '2');
$b = &$a;

$a[0] = '11';
echo $b[0]; // '11'

Comes with solution

$data = array(
    'key' => array(
        'key1' => 'value1'
    )
);

foreach($data as $key => &$obj) {
    $obj['key2'] = 'value2';
}

$data['key']['key2'] == 'value2'; // true

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