class Gem::Commands::InstallCommand

def install_gem(name, version) # :nodoc:
  return if options[:conservative] &&
            !Gem::Dependency.new(name, version).matching_specs.empty?
  req = Gem::Requirement.create(version)
  dinst = Gem::DependencyInstaller.new options
  request_set = dinst.resolve_dependencies name, req
  if options[:explain]
    say "Gems to install:"
    request_set.sorted_requests.each do |activation_request|
      say "  #{activation_request.full_name}"
    end
  else
    @installed_specs.concat request_set.install options
  end
  show_install_errors dinst.errors
end