cpp-variant/test/gtest_variant_printers.h

//
//  gtest_variant_printers.h
//  variant
//
//  Created by Sam Jaffe on 8/14/20.
//  Copyright © 2020 Sam Jaffe. All rights reserved.
//

#pragma once

template <typename K, typename V>
std::ostream & operator<<(std::ostream & os, std::map<K, V> const & value) {
  os << "{";
  if (value.size()) {
    auto it = value.cbegin();
    os << " " << it->first << ":" << it->second;
    for (++it; it != value.cend(); ++it) {
      os << ", " << it->first << ":" << it->second;
    }
  }
  return os << " }";
}

template <std::size_t I, typename ...Ts>
void PrintTo(variant<Ts...> const & value, std::ostream * os) {
  if (value.index() == I) {
    (*os) << value.template get<I>();
  }
}

template <typename ...Ts, std::size_t ...Is>
void PrintTo(variant<Ts...> const & value, std::ostream * os,
             std::index_sequence<Is...>) {
  [[maybe_unused]] auto l = { (PrintTo<Is>(value, os), 0)... };
}

template <typename ...Ts>
void PrintTo(variant<Ts...> const & value, std::ostream * os) {
  if (value.valid()) {
    PrintTo(value, os, std::make_index_sequence<sizeof...(Ts)>());
  } else {
    (*os) << "<invalid>";
  }
}