std_converter.h

  namespace gin {
  
  namespace detail {
  
  // Get a key from `key_val` and check `lookup` for a matching entry.
  // Return true iff a match is found, and set `*out` to the entry's value.
  template <typename KeyType, typename Out, typename Map>
  bool FromV8WithLookup(
      v8::Isolate* isolate,
      v8::Local<v8::Value> key_val,
      const Map& table,
      Out* out,
      std::function<void(KeyType&)> transform = [](KeyType&) {}) {
    static_assert(std::is_same_v<typename Map::mapped_type, Out>);
  
    auto key = KeyType{};
    if (!ConvertFromV8(isolate, key_val, &key))
      return false;
  
    transform(key);
  
    if (const auto* iter = table.find(key); iter != table.end()) {
      *out = iter->second;
      return true;
    }
  
    return false;
  }
  
  }  // namespace detail
  
  // Convert `key_val to a string key and check `lookup` for a matching entry.
  // Return true iff a match is found, and set `*out` to the entry's value.
  template <typename Out, typename Map>
  bool FromV8WithLookup(v8::Isolate* isolate,
                        v8::Local<v8::Value> key_val,
                        const Map& table,
                        Out* out) {
    return detail::FromV8WithLookup<std::string>(isolate, key_val, table, out);
  }
  
  // Convert `key_val to a lowercase string key and check `lookup` for a matching
  // entry. Return true iff a match is found, and set `*out` to the entry's value.
  template <typename Out, typename Map>
  bool FromV8WithLowerLookup(v8::Isolate* isolate,
                             v8::Local<v8::Value> key_val,
                             const Map& table,
                             Out* out) {
    static constexpr auto to_lower_ascii_inplace = [](std::string& str) {
      for (auto& ch : str)
        ch = base::ToLowerASCII(ch);
    };
  
    return detail::FromV8WithLookup<std::string>(isolate, key_val, table, out,
                                                 to_lower_ascii_inplace);
  }