quoted_num for numbers without quotes

[jstkdng]

Hello, my use case is fairly simple, I need to support both quoted numbers and regular numbers when parsing json. I found quoted_num but that always expects quoted numbers and fails on regular numbers. I was thinking of using std::variant but I just want to use the values as ints at the end of the day. Thanks for any response.

struct Command {
    std::string action;
    std::string preview_id;
    std::string image_scaler;

    int x = 0;
    int y = 0;
    int width = 0;
    int height = 0;
};

template <>
struct glz::meta<Command> {
    using T = Command;
    static constexpr auto value = object(
        &T::action,
        &T::preview_id,
        &T::image_scaler,
        "x", glz::quoted_num<&T::x>,
        "y", glz::quoted_num<&T::y>,
        "width", glz::quoted_num<&T::width>,
        "height", glz::quoted_num<&T::height>,
        "max_width", glz::quoted_num<&T::width>,
        "max_height", glz::quoted_num<&T::height>
    );
};

I also need to alias width/height to max_width/max_height and what I have works but I wonder if there is a better solution now.

[stephenberry]

Here is an example that makes use of glz::custom to create custom handling that first tries to parse as a JSON number and then will parse as a JSON string if that fails. (Compiler Explorer Link: https://gcc.godbolt.org/z/Yh57caKvs)

#include <iostream>

#include "glaze/glaze.hpp"

struct Command {
    std::string action;
    std::string preview_id;
    std::string image_scaler;

    int x = 0;
    int y = 0;
    int width = 0;
    int height = 0;
};

template <>
struct glz::meta<Command> {
    using T = Command;

    template <auto MemberPointer>
    static constexpr auto maybe_quoted_int_read = [](T& self, const glz::raw_json& json) {
        // first attempt to parse without quotes
        auto ec = glz::read_json(self.*MemberPointer, json.str);
        if (ec) {
            // if we error then attempt parsing as a quoted number
            ec = glz::read<glz::opts{.quoted_num = true}>(self.*MemberPointer, json.str);
        }
        if (ec) {
            throw std::runtime_error("maybe_quoted_int_read failure");
        }
    };

    template <auto MemberPointer>
    static constexpr auto custom_int = custom<maybe_quoted_int_read<MemberPointer>, MemberPointer>;

    static constexpr auto value = object(
        &T::action,
        &T::preview_id,
        &T::image_scaler,
        "x", custom_int<&T::x>,
        "y", custom_int<&T::y>,
        "width", custom_int<&T::width>,
        "height", custom_int<&T::height>,
        "max_width", custom_int<&T::width>,
        "max_height", custom_int<&T::height>
    );
};

int main() {
    Command obj{};
    std::string input = R"({"x":55,"y":"77"})";
    auto ec = glz::read_json(obj, input);
    if (ec) {
        std::cout << "parse error\n";
    }

    std::cout << glz::write_json(obj).value_or("error") << '\n';

    return 0;
}

Note that glz::custom currently must throw to handle errors. Let me know if this is an issue for you.

[jstkdng]

thanks, this works nice

Note that glz::custom currently must throw to handle errors. Let me know if this is an issue for you

on what situation could that exception appear? I'm trying to write an exception-less project. This is how I'm reading the json currently

template <class T>
using Result = std::expected<T, Error>;

// NOLINTNEXTLINE
#define Err(...) std::unexpected<Error>(std::in_place, std::source_location::current() __VA_OPT__(, ) __VA_ARGS__)

auto Command::from_json(std::string line) -> Result<Command>
{
    Command cmd;
    auto err = glz::read_json(cmd, line);
    if (err) {
        return Err(glz::format_error(err, line));
    }
    return cmd;
}

[stephenberry]

That exception in my example would come from the read_json call.
This is really a flaw in Glaze right now, as it shouldn't require an exception.
An alternative you could use to avoid exceptions is to set your integer to the max integer and treat that as an error condition.
I'll open an issue to add proper error handling to glz::custom, but I won't be able to work on this immediately.