install (Gem::DependencyInstaller)

    # File lib/rubygems/dependency_installer.rb, line 213
      def install dep_or_name, version = Gem::Requirement.default
        if String === dep_or_name then
          find_spec_by_name_and_version dep_or_name, version
        else
          @specs_and_sources = [find_gems_with_sources(dep_or_name).last]
        end

        @installed_gems = []

        gather_dependencies

        @gems_to_install.each do |spec|
          last = spec == @gems_to_install.last
          # HACK is this test for full_name acceptable?
          next if @source_index.any? { |n,_| n == spec.full_name } and not last

          # TODO: make this sorta_verbose so other users can benefit from it
          say "Installing gem #{spec.full_name}" if Gem.configuration.really_verbose

          _, source_uri = @specs_and_sources.assoc spec
          begin
            local_gem_path = Gem::RemoteFetcher.fetcher.download spec, source_uri,
                                                                 @cache_dir
          rescue Gem::RemoteFetcher::FetchError
            next if @force
            raise
          end

          inst = Gem::Installer.new local_gem_path,
                                    :bin_dir             => @bin_dir,
                                    :development         => @development,
                                    :env_shebang         => @env_shebang,
                                    :force               => @force,
                                    :format_executable   => @format_executable,
                                    :ignore_dependencies => @ignore_dependencies,
                                    :install_dir         => @install_dir,
                                    :security_policy     => @security_policy,
                                    :source_index        => @source_index,
                                    :user_install        => @user_install,
                                    :wrappers            => @wrappers,
                                    :skip_dependencies   => @skip_dependencies

          spec = inst.install

          @installed_gems << spec
        end

        @installed_gems
      end