Updating to os 4 5
For more information on changes made to Rails 6.0 please see the release notes.
Webpacker is the default Java Script compiler for Rails 6.
But if you are upgrading the app, it is not activated by default.
If you want to use Webpacker, then include it in your Gemfile and install it: to configure that behavior.
In When using the Classic Autoloader in Rails 6 application it is recommended to set concurrency level to 1 in development environment, for the web servers and background processors, due to the thread-safety concerns.
Rails generally stays close to the latest released Ruby version when it's released: Ruby 1.8.7 p248 and p249 have marshalling bugs that crash Rails.
In classic mode, constant autoloading is not thread-safe, though Rails has locks in place for example to make web requests thread-safe when autoloading is enabled, as it is common in , you won't be able to autoload that file, but eager loading will work because it loads files recursively blindly.
This can be a source of errors if you test things first eager loading, execution may fail later autoloading.
Before attempting to upgrade an existing application, you should be sure you have a good reason to upgrade.
You need to balance several factors: the need for new features, the increasing difficulty of finding support for old code, and your available time and skills, to name a few.
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