libcruft-util/tuple/value.hpp

/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Copyright 2015-2018 Danny Robson <danny@nerdcruft.net>
 */

#ifndef CRUFT_UTIL_TUPLE_VALUE_HPP
#define CRUFT_UTIL_TUPLE_VALUE_HPP

#include "index.hpp"
#include "../types.hpp"

#include <cstddef>
#include <functional>
#include <tuple>
#include <utility>


namespace cruft::tuple::value {
    ///////////////////////////////////////////////////////////////////////////
    /// Call a provided functor of type FunctionT with each value in a
    /// provided tuple-like object TupleT
    template<
        typename FunctionT,
        typename TupleT,
        std::size_t S = 0
    >
    void
    each (FunctionT &&func, TupleT &&value)
    {
        using tuple_t = std::decay_t<TupleT>;
        static_assert (S < std::tuple_size_v<tuple_t>);

        std::invoke (func, std::get<S> (value));

        if constexpr (S + 1 < std::tuple_size_v<tuple_t>) {
            each<FunctionT,TupleT,S+1> (std::forward<FunctionT> (func), std::forward<TupleT> (value));
        }
    }


    ///////////////////////////////////////////////////////////////////////////
    namespace detail {
        template <typename FuncT, typename ArgT, std::size_t ...Indices>
        auto
        map (std::index_sequence<Indices...>, FuncT &&func, ArgT &&arg)
        {
            return std::tuple (std::invoke (func, std::get<Indices> (arg))...);
        }
    };


    /// returns a tuple of the result of applying the provided function to
    /// each value of the supplied tuple.
    template <
        typename FuncT,
        typename ArgT,
        typename IndicesV = std::make_index_sequence<
            std::tuple_size_v<std::decay_t<ArgT>>
        >
    >
    auto map (FuncT &&func, ArgT &&arg)
    {
        return detail::map (IndicesV{}, func, arg);
    }


    ///////////////////////////////////////////////////////////////////////////
    // return a tuple that contains the 'nth' element from each of the supplied
    // tuple-like arguments
    template <size_t N, typename ...TupleT>
    auto
    nth (TupleT&&...args)
    {
        return std::make_tuple (
            std::get<N> (args)...
        );
    }


    ///////////////////////////////////////////////////////////////////////////
    namespace detail {
        template <typename ...TupleT, size_t ...Elements>
        auto
        zip (std::index_sequence<Elements...>, TupleT &&...args)
        {
            return std::make_tuple (
                nth<Elements> (args...)...
            );
        }
    };


    /// converts m arguments of n-tuples into one m-tuple of n-tuples by taking
    /// successive elements from each argument tuple.
    ///
    /// eg, zip (('a', 1.f), (0, nullptr)) becomes (('a', 0), (1.f, nullptr))
    template <typename ...Args >
    auto
    zip (Args &&...args)
    {
        static_assert (sizeof...(args) > 0);
        // ensure all the types have the same static size
        using all_t = std::tuple<std::decay_t<Args>...>;
        using first_t = std::tuple_element_t<0,all_t>;

        static constexpr auto arity = std::tuple_size_v<first_t>;
        static_assert ((
            (arity == std::tuple_size_v<std::decay_t<Args>>) && ...
        ));

        return detail::zip (
            std::make_index_sequence<arity> {},
            std::forward<Args> (args)...
        );
    }


    ///////////////////////////////////////////////////////////////////////////
    namespace detail {
        template <typename TupleT, size_t ...Indices>
        auto
        reverse (index::indices<Indices...>, TupleT &&val)
        {
            return std::make_tuple (
                std::get<Indices> (val)...
            );
        }
    };

    //-------------------------------------------------------------------------
    template <typename TupleT>
    auto
    reverse (TupleT &&val)
    {
        return detail::reverse (
            index::make_reverse_t<
                std::tuple_size_v<std::decay_t<TupleT>>
            > {},
            std::forward<TupleT> (val)
        );
    }
}


#endif