required.hpp

// Copyright (C) 2022 by Camden Mannett.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE or copy at https://www.boost.org/LICENSE_1_0.txt)
 
#pragma once
 
#include "arg_router/exception.hpp"
#include "arg_router/parsing/parsing.hpp"
#include "arg_router/policy/policy.hpp"
 
#include <optional>
 
namespace arg_router::policy
{
template <typename = void>  // This is needed due so it can be used in
class required_t            // template template parameters
{
public:
    constexpr static auto priority = std::size_t{450};
 
    template <typename ValueType, typename... Parents>
    [[noreturn]] ValueType missing_phase([[maybe_unused]] const Parents&... parents) const
    {
        static_assert(sizeof...(Parents) >= 1, "Alias requires at least 1 parent");
 
        using node_type = boost::mp11::mp_first<std::tuple<Parents...>>;
 
        throw multi_lang_exception{error_code::missing_required_argument,
                                   parsing::node_token_type<node_type>()};
    }
};
 
constexpr auto required = required_t<>{};
 
template <typename T>
using is_required = std::is_base_of<required_t<>, T>;
 
template <typename T>
constexpr bool is_required_v = is_required<T>::value;
 
template <>
struct is_policy<required_t<>> : std::true_type {
};
}  // namespace arg_router::policy