class Bundler::Settings

def temporary(update)
  existing = Hash[update.map {|k, _| [k, @temporary[key_for(k)]] }]
  update.each do |k, v|
    set_key(k, v, @temporary, nil)
  end
  return unless block_given?
  begin
    yield
  ensure
    existing.each {|k, v| set_key(k, v, @temporary, nil) }
  end
end