如何利用PHP7的匿名函数和闭包编写更加灵活的代码？

$greet = function ($name) {
    echo "Hello, $name!";
};

$greet('John'); // 输出：Hello, John!

function createGreeting($name) {
    return function () use ($name) {
        echo "Hello, $name!";
    };
}

$greet = createGreeting('John');
$greet(); // 输出：Hello, John!

$numbers = [1, 2, 3, 4, 5];
$double = array_map(function ($num) {
    return $num * 2;
}, $numbers);

print_r($double); // 输出：Array ( [0] => 2 [1] => 4 [2] => 6 [3] => 8 [4] => 10 )

$tasks = ['Task 1', 'Task 2', 'Task 3'];
$callbacks = [];

foreach ($tasks as $task) {
    $callbacks[] = function () use ($task) {
        echo "Processing $task...
";
        // 处理异步任务的代码...
    };
}

foreach ($callbacks as $callback) {
    $callback();
}

function createDatabaseConnection() {
    return function () {
        // 初始化数据库连接...
        return $dbConnection;
    };
}

$getConnection = createDatabaseConnection();

// 在需要使用数据库连接时才调用闭包
$db = $getConnection();
$sql = "SELECT * FROM users";
$result = $db->query($sql);