php - include with nested round brackets

Question

What does the code below means in PHP7:

(require __DIR__ . '/routes.php')($app);

And how to convert it to non-Uniform syntax?

routes.php content:

use SlimApp;

return function (App $app) {
    // empty
};```

question from:https://stackoverflow.com/questions/65853371/include-with-nested-round-brackets

Answer 1

require/include/eval behave like expressions, specifically when the invoked code/file returns something. In this case the return value is used as a function expression. It's equivalent to:

$return = (require "file.php");
${NULL} = $return($app);