boost_describe 0.1.0

// Copyright 2020 Peter Dimov
// Distributed under the Boost Software License, Version 1.0.
// https://www.boost.org/LICENSE_1_0.txt

#include <boost/describe.hpp>
#include <boost/mp11.hpp>
#include <boost/json.hpp>
#include <boost/type_traits.hpp>
#include <boost/utility/string_view.hpp>
#include <stdexcept>
#include <string>

template<class C1, class C2, class R, class... A, std::size_t... I>
  boost::json::value
    call_impl_( C1 & c1, R (C2::*pmf)(A...), boost::json::array const & args,
      std::index_sequence<I...> )
{
    return boost::json::value_from(
      (c1.*pmf)(
        boost::json::value_to< boost::remove_cv_ref_t<A> >( args[ I ] )... ) );
}

template<class C1, class C2, class R, class... A>
  boost::json::value
    call_impl( C1 & c1, R (C2::*pmf)(A...), boost::json::array const & args )
{
    if( args.size() != sizeof...(A) )
    {
        throw std::invalid_argument( "Invalid number of arguments" );
    }

    return call_impl_( c1, pmf, args, std::index_sequence_for<A...>() );
}

template<class C>
  boost::json::value
    call( C & c, boost::string_view method, boost::json::array const & args )
{
    using Fd = boost::describe::describe_members<C,
        boost::describe::mod_public | boost::describe::mod_function>;

    bool found = false;
    boost::json::value result;

    boost::mp11::mp_for_each<Fd>([&](auto D){

        if( !found && method == D.name)
        {
            result = call_impl( c, D.pointer, args );
            found = true;
        }

    });

    if( !found )
    {
        throw std::invalid_argument( "Invalid method name" );
    }

    return result;
}

struct Object
{
    std::string greet( std::string const & who )
    {
        return "Hello, " + who + "!";
    }

    int add( int x, int y )
    {
        return x + y;
    }
};

BOOST_DESCRIBE_STRUCT(Object, (), (greet, add))

#include <iostream>

int main()
{
    Object obj;
    std::cout << call( obj, "greet", { "world" } ) << std::endl;
    std::cout << call( obj, "add", { 1, 2 } ) << std::endl;
}