mountcontrol/cxx/mcc_traits.h

#pragma once

#include <chrono>
#include <format>
#include <ranges>

namespace mcc::traits
{

template <typename R>
concept mcc_char_view = std::ranges::view<R> && std::same_as<std::ranges::range_value_t<R>, char>;


// input range of char/const char
template <typename R, typename CharT = char>
concept mcc_input_char_range =
    std::ranges::input_range<R> && std::is_same_v<std::remove_cv_t<std::ranges::range_value_t<R>>, CharT>;


// output range of char/const char
template <typename R, typename CharT = char>
concept mcc_output_char_range =
    std::ranges::output_range<R, CharT> && std::same_as<std::remove_cv_t<std::ranges::range_value_t<R>>, CharT>;


template <typename R>
concept mcc_view_or_output_char_range = mcc_char_view<R> || mcc_output_char_range<R>;


template <typename R>
concept mcc_range_of_input_char_range =
    std::ranges::range<R> && traits::mcc_input_char_range<std::ranges::range_value_t<R>>;


template <typename R>
concept mcc_range_of_output_char_range =
    std::ranges::range<R> && traits::mcc_output_char_range<std::ranges::range_value_t<R>>;



// https://stackoverflow.com/questions/72430369/how-to-check-that-a-type-is-formattable-using-type-traits-concepts)
template <typename T>
concept mcc_formattable =
    requires(T v, std::format_context ctx) { std::formatter<std::remove_cvref_t<T>>().format(v, ctx); };


// from https://stackoverflow.com/questions/74383254/concept-that-models-only-the-stdchrono-duration-types
template <typename T>
concept mcc_time_duration_c = requires {
    []<class Rep, class Period>(std::type_identity<std::chrono::duration<Rep, Period>>) {

    }(std::type_identity<std::remove_cvref_t<T>>());
};


template <typename T>
concept mcc_systime_c = requires {
    []<class DT>(std::type_identity<std::chrono::sys_time<DT>>) {}(std::type_identity<std::remove_cvref_t<T>>());
};


/*  a callable concept and its signature traits   */

template <typename T>
concept mcc_is_callable = std::is_function_v<T> || (std::is_object_v<T> && requires(T) { &T::operator(); });


// helper classes for callable signature deducing
template <typename... Ts>
struct mcc_func_traits_helper_t;

template <typename R>
struct mcc_func_traits_helper_t<R> {
    using ret_t = R;
    using args_t = std::tuple<>;
    using arg1_t = void;
    static constexpr size_t arity = 0;
};

template <typename R, typename Arg, typename... Args>
struct mcc_func_traits_helper_t<R, Arg, Args...> {
    using ret_t = R;
    using args_t = std::tuple<Arg, Args...>;
    using arg1_t = Arg;
    static constexpr size_t arity = sizeof...(Args) + 1;
};

template <typename F>
struct mcc_func_traits {
    // use of an empty struct here to match std::invoke_result behaivior (at least of GCC)
};

template <typename R, typename... Args>
struct mcc_func_traits<R (*)(Args...)> : mcc_func_traits_helper_t<R, Args...> {
};

template <typename R, typename... Args>
struct mcc_func_traits<R(Args...)> : mcc_func_traits_helper_t<R, Args...> {
};

template <typename C, typename R, typename... Args>
struct mcc_func_traits<R (C::*)(Args...)> : mcc_func_traits_helper_t<R, Args...> {
};

template <typename C, typename R, typename... Args>
struct mcc_func_traits<R (C::*)(Args...) const> : mcc_func_traits_helper_t<R, Args...> {
};

template <typename F>
    requires mcc_is_callable<F>
struct mcc_func_traits<F> : mcc_func_traits<decltype(&F::operator())> {
};

// reference/const ref and rvalue helpers
template <typename F>
struct mcc_func_traits<F&> : mcc_func_traits<F> {
};

template <typename F>
struct mcc_func_traits<const F&> : mcc_func_traits<F> {
};

template <typename F>
struct mcc_func_traits<F&&> : mcc_func_traits<F> {
};

// type of the returned value
template <typename T>
using mcc_retval_t = typename mcc_func_traits<T>::ret_t;

// type of the first argument of callable
template <typename T>
using mcc_func_arg1_t = typename mcc_func_traits<T>::arg1_t;

// type of the N-th argument of callable
// NOTE: starts from 1 not from 0!!!
template <typename T, size_t N = 1>
using mcc_func_argN_t = std::conditional_t<N >= mcc_func_traits<T>::arity,
                                           std::tuple_element_t<N - 1, typename mcc_func_traits<T>::args_t>,
                                           void>;


// non-const lvalue reference, constructible from CtorArgTs (an output argument of function)
template <typename T, typename... CtorArgTs>
concept mcc_output_arg_c = !std::is_const_v<std::remove_reference_t<T>> && std::is_lvalue_reference_v<T> &&
                           std::constructible_from<std::remove_reference_t<T>, CtorArgTs...>;



// std::tuple or std::pair
template <typename T>
concept mcc_tuple_c = requires {
    requires requires {
        []<typename... Ts>(std::type_identity<std::tuple<Ts...>>) {}(std::type_identity<std::remove_cvref_t<T>>());
    } || requires {
        []<typename T1, typename T2>(std::type_identity<std::pair<T1, T2>>) {
        }(std::type_identity<std::remove_cvref_t<T>>());
    };
};


template <typename T>
concept mcc_nonconst_ref = std::is_lvalue_reference_v<T> && !std::is_const_v<std::remove_reference_t<T>>;

namespace details
{

// compile-time hash for type
// (from https://stackoverflow.com/questions/56292104/hashing-types-at-compile-time-in-c17-c2a)
// WARNING: it does not work for unnamed struct!!!
template <typename T>
static consteval size_t Hash()
{
    size_t result{};

#ifdef _MSC_VER
    for (const auto& c : __FUNCSIG__)
#else  // GCC and clang
    for (const auto& c : __PRETTY_FUNCTION__)
#endif
        (result ^= c) <<= 1;

    return result;
}

}  // namespace details

template <typename T>
static constexpr size_t mcc_type_hash = details::Hash<T>();

static constexpr size_t mcc_hash_combine(size_t lhs, size_t rhs)
{
    constexpr size_t v_const = sizeof(size_t) >= 8 ? 0x517cc1b727220a95 : 0x9e3779b9;

    lhs ^= rhs + v_const + (lhs << 6) + (lhs >> 2);

    return lhs;
}

template <typename T1, typename T2>
static constexpr size_t mcc_type_pair_hash()
{
    return mcc_hash_combine(mcc_type_hash<T1>, mcc_type_hash<T2>);
}

}  // namespace mcc::traits