C++ (Cpp) optional::parent_path示例

void expander::expand(
    const boost::optional<boost::filesystem::path>& template_path,
    dynamic::object& o) const {

    BOOST_LOG_SEV(lg, debug) << "Before expansion: " << o;

    if (!template_path) {
        BOOST_LOG_SEV(lg, debug)
            << "No template path supplied so not performing expansion";
        return;
    }

    BOOST_LOG_SEV(lg, debug) << "Template path: "
                             << template_path->generic_string();

    std::string output_filename(template_path->stem().generic_string());
    output_filename += stitch_postfix;

    const dynamic::field_selector fs(o);
    boost::filesystem::path absolute_output_directory;
    if (fs.has_field(traits::relative_output_directory())) {
        const auto tc(fs.get_text_content(traits::relative_output_directory()));
        using namespace boost::filesystem;
        path rel_dir(tc);
        absolute_output_directory = absolute(rel_dir,
            template_path->parent_path());
    } else
        absolute_output_directory = template_path->parent_path();

    absolute_output_directory /= output_filename;

    const dynamic::field_instance_factory f;
    const auto v(f.make_text(absolute_output_directory.generic_string()));
    o.fields()[traits::output_path()] = v;

    BOOST_LOG_SEV(lg, debug) << "After expansion: " << o;
}