Better support for SAX style serialize and deserialize in new version?

[salutant]

it is very useful to do a language binding , Currently we need iterate the object to create a temp cpp json object before serizalize to string .

[nlohmann]

Can you be more specific?

[salutant]

if i want to use this to create a json serializer and deserializer for other language like lua.
in lua to serialize a lua table to string , i need to do iterate lua table to create a temp cpp json object first, then use it's dump() method to string.

rapidjson give a rapidjson::Writer class . with this we can serialize a lua table to string directly in iterating lua table.

https://github.com/xpol/lua-rapidjson this project create a lua json serializer and deserializer use rapidjson maybe can help you .

[nlohmann]

The link is dead. I still don't understand your use case.

You want to iterate over a Lua table and create a JSON serialization from it? But you want to do this without creating an internal JSON representation from the Lua table?

[salutant]

sorry , the link is okay now,
i want to explain my idea clearly, but i think i couldn't, so i write some code

class lua_json_writer
{
public:
	lua_json_writer(lua_State * l, int idx)
		: L(l), index_(idx), writer_(buffer_)
	{}
	~lua_json_writer()
	{}

	const char * encode()
	{
		encode_table(index_);
		return buffer_.GetString();
	}

private:
	void encode_value(int val)
	{
		int t = lua_type(L, val);
		if ( t == LUA_TSTRING ) {
			size_t len = 0;
			const char * str = lua_tolstring(L, val, &len);
			writer_.String(str, len);
		} else if ( t == LUA_TNUMBER ) {
			if ( lua_isinteger(L, val) ) {
				writer_.Int64(lua_tointeger(L, val));
			} else {
				writer_.Double(lua_tonumber(L, val));
			}
		} else if ( t == LUA_TBOOLEAN ) {
			writer_.Bool(!!lua_toboolean(L, val));
		} else if ( t == LUA_TTABLE ) {
			encode_table(val);
		}
	}

	void encode_object(int key, int val)
	{
		const char * key_str = lua_tostring(L, key);
		if ( strcmp(key_str, "__type") == 0 ) {
			return;
		}
		writer_.Key(key_str);
		encode_value(val);
	}

	void encode_array(int key, int val)
	{
		if ( lua_type(L, key) != LUA_TNUMBER ) {
			return;
		}

		encode_value(val);
	}

	void for_each(std::function<void(lua_json_writer&, int, int)> fx)
	{
		for ( lua_pushnil(L); lua_next(L, -2) != 0; lua_pop(L, 1) ) {

			int top = lua_gettop(L);
			fx(*this, top - 1, top);
		}
	}

	void encode_table(int idx)
	{
		int t = 1; //
		lua_getfield(L, idx, "__type");
		if ( !lua_isnil(L, -1) ) {
			t = static_cast<int>(lua_tointeger(L, -1));
		}
		lua_pop(L, 1);

		if ( t == 1 ) {
			writer_.StartObject();
			for_each(&lua_json_writer::encode_object);
			writer_.EndObject();
		} else if ( t == 2 ) {
			writer_.StartArray();
			for_each(&lua_json_writer::encode_array);
			writer_.EndArray();
		} else if ( t == 3 ) {
			writer_.Null();
		}
	}

private:
	lua_State * L;
	int	index_;
	rapidjson::StringBuffer buffer_; //
	rapidjson::Writer<rapidjson::StringBuffer, rapidjson::UTF8<>, rapidjson::ASCII<>> writer_; //
};

this code can serialize a lua table to json string , i want json.hpp can do something like this .

[nlohmann]

You can convert arbitrary types from/to json with the techniques described in https://github.com/nlohmann/json#arbitrary-types-conversions. But if I understand you correctly, you do not want to create a json object, but directly a JSON compliant string representation from you Lua array, right?

[salutant]

yes i don't want to create json object

[nlohmann]

But how would this library help you if you do not want to use any of its functions?

[salutant]

alright , the rapidjson given rapidjson::Reader and rapidjson::Writer could do this .
cos i like this library so i want to do it use this . if couldn't i'll give up .
thanks!

[nlohmann]

I do not understand how exactly my library could help you. We provide a C++-style API for JSON values, support to create these values from arbitrary types, and also the possibility to serialize them. But it seems that you need a translation from Lua types to JSON string. This can be implemented manually without the need of any third-party library.

And why exactly don't you want to create an temporary object in the first place? Performance?

[nlohmann]

FYI: #971