class CppFiles(datatype('CppFiles', [
    'root_dir',
    'file_paths',
])):

  def __new__(cls, root_dir, file_paths):
    if not os.path.isdir(root_dir):
      raise CppFilesError("root dir '{}' does not exist!"
                          .format(root_dir))

    for rel_path in file_paths:
      abs_path = os.path.join(root_dir, rel_path)
      if not os.path.isfile(abs_path):
        raise CppFilesError("rel path '{}' is not a file (from cwd '{}')"
                            .format(root_dir, rel_path))

    return super(CppFiles, cls).__new__(cls, root_dir, file_paths)

class CppFileProvider(object):

  @abstractmethod
  def as_cpp_files(self): pass

  def as_path_globs(self):
    cpp_files = self.as_cpp_files()
    return PathGlobs.create(cpp_files.root_dir, include=cpp_files.file_paths)