Symfony Flex is a Composer plugin for Symfony. It automates the most common tasks of Symfony applications, like installing and removing bundles and other Composer dependencies.
Link: https://flex.symfony.com/
This site allows us to run this command:
composer require mailer
On this site you can find recipe by alias. For example, mailer is alias for symfony/swiftmailer-bundle.
In your project symfony.lock will be created. This file is managed by Flex.
It keeps track of which recipes have been installed.
Whenever you install a package, Flex will execute the recipe for that package, if there is one.
Recipes can add configuration files, create directories, or even modify files like .gitignore
or config/bundles.php so that the library instantly works without any extra setup.