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fix: nlohmann::adl_serializer for std::optional (#9147)

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This allows templates such as `NLOHMANN_DEFINE_TYPE_*` templates and other generators with things like `std::vector<std::optional<T>>`.

Co-authored-by: John Ericson <John.Ericson@Obsidian.Systems>
This commit is contained in:
Alex Ameen 2023-11-29 19:26:39 -06:00 • committed by GitHub
parent a8fea5a54f
commit 02bd821f2e
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2 changed files with 72 additions and 5 deletions
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19
src/libutil/json-utils.hh
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@ -78,20 +78,29 @@ namespace nlohmann {
*/
template<typename T>
struct adl_serializer<std::optional<T>> {
static std::optional<T> from_json(const json & json) {
/**
* @brief Convert a JSON type to an `optional<T>` treating
* `null` as `std::nullopt`.
*/
static void from_json(const json & json, std::optional<T> & t) {
static_assert(
nix::json_avoids_null<T>::value,
"null is already in use for underlying type's JSON");
return json.is_null()
t = json.is_null()
? std::nullopt
: std::optional { adl_serializer<T>::from_json(json) };
: std::make_optional(json.template get<T>());
}
static void to_json(json & json, std::optional<T> t) {
/**
* @brief Convert an optional type to a JSON type treating `std::nullopt`
* as `null`.
*/
static void to_json(json & json, const std::optional<T> & t) {
static_assert(
nix::json_avoids_null<T>::value,
"null is already in use for underlying type's JSON");
if (t)
adl_serializer<T>::to_json(json, *t);
json = *t;
else
json = nullptr;
}