Cannot create shared_ptr with custom traits value

[golxzn]

Hi 👋

I've implemented my own trait like that:

template<class T>
struct CustomTraits : public tao::json::traits<T> {
	TAO_JSON_DEFAULT_KEY("custom");
};

template<> struct CustomTraits<SDL_FPoint> {
	TAO_JSON_DEFAULT_KEY("point");

	template<template<class...> class Traits>
	static void assign(tao::json::basic_value<Traits> &value, const SDL_FPoint &point);

	template<template<class...> class Traits>
	static SDL_FPoint as(const tao::json::basic_value<Traits> &value);

	template<template<class...> class Traits>
	static void to(const tao::json::basic_value<Traits> &value, SDL_FPoint &point);

	template<template<class...> class Traits>
	static bool equal(const tao::json::basic_value<Traits> &value, const SDL_FPoint &point) noexcept;

	template<template<class...> class Traits>
	static bool less_than(const tao::json::basic_value<Traits> &value, const SDL_FPoint &point) noexcept;

	template<template<class...> class Traits>
	static bool greater_than(const tao::json::basic_value<Traits> &value, const SDL_FPoint &point) noexcept;

	template<template<class...> class Traits, class Consumer>
	static void produce(Consumer &c, const SDL_FPoint &point);
};

template<class T>
using custom_trait = CustomTraits<T>;
using custom_value = tao::json::basic_value<CustomTraits>;

PS: (I hided the implementations to make this question shorter)

So, I'm trying to read the file and initialize my custom_value as a shared pointer:

std::shared_ptr<custom_value> config{};
if (fs::ifstream file{ origin, std::ios::binary | std::ios::ate }; file) {
	const auto size{ file.tellg() };
	file.seekg(std::ios::beg);
	std::string content(size, '\0');
	file.read(&content[0], size);
	config = std::make_shared<custom_value>(
		tao::json::basic_from_string<custom_traits>(std::move(content))
	);
}

But I get a lot of template errors. They are about error C2672: 'std::construct_at': no matching overloaded function found which means that the object custom_value doesn't have move constructor, but it has.

Before this error, I'd gotten the error inside tao::json::internal::pair that it cannot find an implementation of Traits< std::decay_t< U > >::template default_key< Traits >::as_string(), so I added TAO_JSON_DEFAULT_KEY into my traits classes.

Please, could you help me to initialize my custom tao::json::basic_value<CustomTraits> for the shared pointer for managing resources better.

[golxzn]

Oh. And tao::json::basic_from_file and tao::json::basic_from_stream don't work too.

[ColinH]

First, this problem has nothing to do with std::shared_ptr. Second, it works for me when I use tao::json::basic_from_string<CustomTraits> instead of tao::json::basic_from_string<custom_trait>.

The type alias custom_trait doesn't add anything, and I'm not really surprised that your example doesn't work given that templated type aliases aren't quite a replacement for class templates like normal type aliases are for classes/types, though I would have expected some different error.

And third, basic_from_file and basic_from_stream also work when using CustomTraits instead of custom_trait. Does this small change work for you, too?

[golxzn]

Yeah, sorry. I realized that the tao::json::basic_from_string template doesn't work with such type aliases
Thank you