Ruby Regex Supports Interpolation

Today we built a Ruby regex that included an interpolated string. It looked like this:

# app/models/developer.rb
validates :email, format: { with: /\A.+@(#{ENV['permitted_domains']})\z/ }

This allows permitted_domains to be customized as an environmental variable:

# config/application.yml
permitted_domains: 'hashrocket.com|hshrckt.com'

The parens and pipe allow us to white-list multiple domains in a single environmental variable.