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 <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);
  }
 
  namespace detail {
 
    // Helper function to read a std::variant from HDF5.
    template <typename VT, typename U, typename... Ts>
    void h5_read_variant_helper(VT &v, datatype dt, group g, std::string const &name) {
      // finds the correct h5_read recursively
      if (hdf5_type_equal(hdf5_type<U>(), dt)) {
        v = VT{h5_read<U>(g, name)};
        return;
      }
      if constexpr (sizeof...(Ts) > 0)
        h5_read_variant_helper<VT, Ts...>(v, dt, g, name);
      else
        throw std::runtime_error("Error in h5_read_variant_helper: Type stored in the variant has no corresponding HDF5 datatype");
    }
 
  } // namespace detail
 
  template <typename... Ts>
  void h5_read(group g, std::string const &name, std::variant<Ts...> &v) {
    // name is a group --> triqs object
    // assume for the moment, name is a dataset.
    dataset ds  = g.open_dataset(name);
    datatype dt = get_hdf5_type(ds);
    detail::h5_read_variant_helper<std::variant<Ts...>, Ts...>(v, dt, g, name);
  }
 
} // namespace h5
 
#endif // LIBH5_STL_VARIANT_HPP