source 'https://rubygems.org' git_source(:github) { |repo_name| "https://github.com/#{repo_name}" } def gem_installed?(args) name, *version = *args dependency = Gem::Dependency.new(name, *version) specs = dependency.matching_specs specs && !specs.empty? end def optional_gem(*args) gem(*args) if gem_installed?(args) end # database adapters optional_gem 'therubyracer', platform: :ruby optional_gem 'therubyrhino', platform: :jruby # Specify your gem's dependencies in google-web-translate.gemspec gemspec