variant.hpp

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// Copyright (c) 2019-2024 Simons Foundation
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0.txt
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Authors: Thomas Hahn, Olivier Parcollet, Nils Wentzell

 
#ifndef LIBH5_STL_VARIANT_HPP
#define LIBH5_STL_VARIANT_HPP
 
#include "../format.hpp"
#include "../generic.hpp"
#include "../group.hpp"
#include "./string.hpp"
 
#include <stdexcept>
#include <string>
#include <type_traits>
#include <variant>
 
namespace h5 {


  template <typename... T>
  struct hdf5_format_impl<std::variant<T...>> {
    static std::string invoke() = delete;
  };

  template <typename... Ts>
  void h5_write(group g, std::string const &name, std::variant<Ts...> const &v) {
    std::visit([&](auto const &x) { h5_write(g, name, x); }, v);
  }

  template <typename T, typename... Ts>
  void h5_read(group g, std::string const &name, std::variant<T, Ts...> &v) {
    dataset ds    = g.open_dataset(name);
    datatype dt   = get_hdf5_type(ds);
    auto try_read = [&]<typename U>(std::type_identity<U>) {
      if (!hdf5_type_equal(hdf5_type<U>(), dt)) return false;
      v = h5_read<U>(g, name);
      return true;
    };
    if ((try_read(std::type_identity<T>{}) || ... || try_read(std::type_identity<Ts>{}))) return;
    throw std::runtime_error("Error in h5_read for std::variant: stored HDF5 datatype matches no variant alternative (allowed: "
                             + (get_name_of_h5_type<T>() + ... + (", " + get_name_of_h5_type<Ts>())) + ")");
  }

  template <typename... Ts>
  void h5_write_attribute(object obj, std::string const &name, std::variant<Ts...> const &v) {
    std::visit([&](auto const &x) { h5_write_attribute(obj, name, x); }, v);
  }

  template <typename T, typename... Ts>
  void h5_read_attribute(object obj, std::string const &name, std::variant<T, Ts...> &v) {
    datatype dt   = get_hdf5_attribute_type(obj, name);
    auto try_read = [&]<typename U>(std::type_identity<U>) {
      if (!hdf5_type_equal(hdf5_type<U>(), dt)) return false;
      v = h5_read_attribute<U>(obj, name);
      return true;
    };
    if ((try_read(std::type_identity<T>{}) || ... || try_read(std::type_identity<Ts>{}))) return;
    throw std::runtime_error("Error in h5_read_attribute for std::variant: stored HDF5 datatype matches no variant alternative (allowed: "
                             + (get_name_of_h5_type<T>() + ... + (", " + get_name_of_h5_type<Ts>())) + ")");
  }

 
} // namespace h5
 
#endif // LIBH5_STL_VARIANT_HPP