utility.hpp

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// Copyright (c) 2023-2025 Jakub Musiał
// This file is part of the CPP-AP project (https://github.com/SpectraL519/cpp-ap).
// Licensed under the MIT License. See the LICENSE file in the project root for full license information.
 
#pragma once
 
#include "ap/action/specifiers.hpp"
 
#include <utility>
#include <variant>
 
namespace ap::action::detail {
 
template <typename AS>
concept c_value_action_specifier =
    ap::detail::c_one_of<AS, action_type::observe, action_type::transform, action_type::modify>;
 
template <typename AS>
concept c_action_specifier = c_value_action_specifier<AS> or std::same_as<AS, action_type::on_flag>;
 
template <c_value_action_specifier AS, ap::detail::c_argument_value_type T>
using callable_type = typename AS::template type<T>;
 
template <ap::detail::c_argument_value_type T>
using value_action_variant_type = std::variant<
    callable_type<action_type::observe, T>,
    callable_type<action_type::transform, T>,
    callable_type<action_type::modify, T>>;
 
template <ap::detail::c_argument_value_type T>
struct apply_visitor {
    using value_type = T;
 
    void operator()(const callable_type<action_type::observe, value_type>& action) const {
        action(std::as_const(value));
    }
 
    void operator()(const callable_type<action_type::transform, value_type>& action) const {
        value = action(std::as_const(value));
    }
 
    void operator()(const callable_type<action_type::modify, value_type>& action) const {
        action(value);
    }
 
    value_type& value; 
};
 
} // namespace ap::action::detail