PHP how to import all classes from another namespace

This is not possible in PHP.

All you can do is:

namespace Foo;

use Bar;

$obj = new Bar\SomeClassFromBar();

You can use the "as" for shortening and aliasing long namespaces

composer.json

{
    "autoload": {
        "psr-4": {
            "Lorem\\Ipsum\\": "lorem/ipsum",
            "Lorem\\Ipsum\\Dolor\\": "lorem/ipsum/dolor",
            "Lorem\\Ipsum\\Dolor\\Sit\\": "lorem/ipsum/dolor/sit"
        }
    }
}  

index.php

    <?php

    use Lorem\Ipsum\Dolor\Sit as FOO;

    define ('BASE_PATH',dirname(__FILE__));
    require BASE_PATH.DIRECTORY_SEPARATOR.'vendor'.DIRECTORY_SEPARATOR.'autoload.php';

    $bar = new FOO\Bar();
    $baz = new FOO\Baz();
    $qux = new FOO\Qux();