eldritch horrors
c208e918e5
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>
(cherry picked from commit 02bd821f2e71372d31bbe6700bd68086cc2ee70a)
Change-Id: I8b0ebcf2af4226610dadd565962f2d2327415a03
110 lines
2.9 KiB
C++
110 lines
2.9 KiB
C++
#pragma once
|
|
///@file
|
|
|
|
#include <nlohmann/json.hpp>
|
|
#include <list>
|
|
|
|
namespace nix {
|
|
|
|
const nlohmann::json * get(const nlohmann::json & map, const std::string & key);
|
|
|
|
nlohmann::json * get(nlohmann::json & map, const std::string & key);
|
|
|
|
/**
|
|
* Get the value of a json object at a key safely, failing
|
|
* with a Nix Error if the key does not exist.
|
|
*
|
|
* Use instead of nlohmann::json::at() to avoid ugly exceptions.
|
|
*
|
|
* _Does not check whether `map` is an object_, use `ensureType` for that.
|
|
*/
|
|
const nlohmann::json & valueAt(
|
|
const nlohmann::json & map,
|
|
const std::string & key);
|
|
|
|
/**
|
|
* Ensure the type of a json object is what you expect, failing
|
|
* with a Nix Error if it isn't.
|
|
*
|
|
* Use before type conversions and element access to avoid ugly exceptions.
|
|
*/
|
|
const nlohmann::json & ensureType(
|
|
const nlohmann::json & value,
|
|
nlohmann::json::value_type expectedType);
|
|
|
|
/**
|
|
* For `adl_serializer<std::optional<T>>` below, we need to track what
|
|
* types are not already using `null`. Only for them can we use `null`
|
|
* to represent `std::nullopt`.
|
|
*/
|
|
template<typename T>
|
|
struct json_avoids_null;
|
|
|
|
/**
|
|
* Handle numbers in default impl
|
|
*/
|
|
template<typename T>
|
|
struct json_avoids_null : std::bool_constant<std::is_integral<T>::value> {};
|
|
|
|
template<>
|
|
struct json_avoids_null<std::nullptr_t> : std::false_type {};
|
|
|
|
template<>
|
|
struct json_avoids_null<bool> : std::true_type {};
|
|
|
|
template<>
|
|
struct json_avoids_null<std::string> : std::true_type {};
|
|
|
|
template<typename T>
|
|
struct json_avoids_null<std::vector<T>> : std::true_type {};
|
|
|
|
template<typename T>
|
|
struct json_avoids_null<std::list<T>> : std::true_type {};
|
|
|
|
template<typename K, typename V>
|
|
struct json_avoids_null<std::map<K, V>> : std::true_type {};
|
|
|
|
}
|
|
|
|
namespace nlohmann {
|
|
|
|
/**
|
|
* This "instance" is widely requested, see
|
|
* https://github.com/nlohmann/json/issues/1749, but momentum has stalled
|
|
* out. Writing there here in Nix as a stop-gap.
|
|
*
|
|
* We need to make sure the underlying type does not use `null` for this to
|
|
* round trip. We do that with a static assert.
|
|
*/
|
|
template<typename T>
|
|
struct adl_serializer<std::optional<T>> {
|
|
/**
|
|
* @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");
|
|
t = json.is_null()
|
|
? std::nullopt
|
|
: std::make_optional(json.template get<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)
|
|
json = *t;
|
|
else
|
|
json = nullptr;
|
|
}
|
|
};
|
|
|
|
}
|