Closure.php

$db = function ($request, Closure $next) {
    echo '成功建立数据库连接' . PHP_EOL;
    $response = $next($request);
    echo '成功关闭数据库连接' . PHP_EOL;

    return $response;
};

$like = function ($request, Closure $next) {
    echo '点赞+1' . PHP_EOL;
    $response = $next($request);
    echo '点赞+2' . PHP_EOL;

    return $response;
};

$app = function ($request) {
    echo $request . PHP_EOL;
    return '一个无聊的返回值';
};

$allMiddleware = [$like, $db];
$next = $app;
foreach ($allMiddleware as $middleware) {
    $next = function ($request) use ($middleware, $next) {
        return $middleware($request, $next);
    };
}

$response = $next('O(∩_∩)O');
echo $response;