This is an opinionated gist just to show that it's possible to start a ruby gem development work using Docker (I don't want any ruby installation in my manjaro laptop).
To generate a new gem in linux you can use the following command (if you're using MacOS there is no need to use --user
flag):
docker run --rm -it -w /app -v ${PWD}:/app ruby:slim bash -c "bundle gem newgem && chown -R $(id -u):$(id -g) ./newgem"
Then you can use the following Dockerfile to start the gem development work: