PHP高级特性：数组与集合的深入探索

$tree = array(
    'level1' => array(
        'level2' => array(
            'data' => 'value'
        )
    )
);

array_walk_recursive($tree, function($value, $key) {
    echo "$key: $value\n";
});

$assoc = array(
    'name' => 'John Doe',
    'age' => 30
);

if ($assoc['name'] == 'John Doe') {
    echo 'Name matches';
}

$numbers = array(1, 2, 3, 4, 5);

$filteredNumbers = array_filter($numbers, function($num) {
    return $num % 2 == 0;
});

$collection = Collection::make(['foo', 'bar', 'baz']);

$filteredCollection = $collection->filter(function($item) {
    return is_string($item);
});

$mappedCollection = $collection->map(function($item) {
    return strtoupper($item);
});

$sum = $collection->sum();
$average = $collection->average();

$tree = array();
$tree['root'] = array(
    'left' => array(
        'data' => 'left branch'
    ),
    'right' => array(
        'data' => 'right branch'
    )
);

array_walk_recursive($tree, function($value, $key) {
    if ($value != 'root') {
        echo "$key: $value\n";
    }
});

$users = [
    ['name' => 'John Doe', 'age' => 30],
    ['name' => 'Jane Doe', 'age' => 25],
];

$collection = Collection::make($users);

$filteredCollection = $collection->filter(function($user) {
    return $user['age'] > 25;
});

$mappedCollection = $collection->map(function($user) {
    return $user['name'];
});