This provides a few benefits:
- faster `brew cask` execution times as another Ruby process is not
needed. Cask can instead be loaded in-process with Homebrew. This
will also make it easier to use some of Homebrew's core code and
ease moving code from Cask into Homebrew core.
- Users do not need to `brew upgrade` Cask any more: it's done
automatically on any `brew update` or `git pull` of the Cask tap.
Vítor Galvão