Example uses of Slim 3's container

slim-container-examples.php

<?php
// All file paths relative to root
chdir(dirname(__DIR__));
require "vendor/autoload.php";

$settings = ['foo' => 'FOO', 'bar' => 'BAR'];
$app = new \Slim\App($settings);


// Set some things into the container
$container = $app->getContainer();

$container['App\Controller\BookController'] = function ($c) {
    return new App\Controller\BookController();
};

$container['MyRouteMiddleware'] = function ($c) {
    return function ($request, $response, $next) use ($c) {
        $settings = $c['settings'];
        // do something with $settings
        return $next($request, $response);
    };
};


// Routing

// Home page...
$app->get(
    '/',
    function ($request, $response) {
        // access container via __get:
        $foo = $this->settings['foo'];

        // or via getContainer()
        $container = $this->getContainer();
        $bar = $container['settings']['bar'];

        $response->write("<p>Hello World</p>");
        return $response;
    }
)
// ... with some middleware
->add(function ($request, $response, $next) use ($container) {
    $middlware = $container['MyRouteMiddleware'];
    return $middlware($request, $response, $next);
});

// Another page
$app->map(
    ['GET', 'POST'],
    '/book/edit/{id}',
    'App\Controller\BookController:edit'
);

$app->run();

For PHP-DI in Slim 4, look up how PHP-DI's container builder works.

addDefinitions() takes an array, so you can just add to the list of things it knows about. I don't know how it expects a factory to be registered.