87 lines
2.9 KiB
C++
87 lines
2.9 KiB
C++
#pragma once
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#include <tuple>
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#include <type_traits>
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namespace kpn {
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// ── Primary template — not defined; only specialisations match ────────────────
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template<typename F>
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struct function_traits;
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// Free function
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template<typename R, typename... Args>
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struct function_traits<R(Args...)> {
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using return_t = R;
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using args = std::tuple<Args...>;
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static constexpr std::size_t arity = sizeof...(Args);
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};
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// Function pointer
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template<typename R, typename... Args>
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struct function_traits<R(*)(Args...)> : function_traits<R(Args...)> {};
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// Member function pointer (const)
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template<typename C, typename R, typename... Args>
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struct function_traits<R(C::*)(Args...) const> : function_traits<R(Args...)> {};
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// Member function pointer (non-const)
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template<typename C, typename R, typename... Args>
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struct function_traits<R(C::*)(Args...)> : function_traits<R(Args...)> {};
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// Callable (lambda / std::function) — delegate to operator()
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template<typename F>
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struct function_traits : function_traits<decltype(&F::operator())> {};
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// ── Helpers ───────────────────────────────────────────────────────────────────
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template<typename F>
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using return_t = typename function_traits<std::remove_cvref_t<F>>::return_t;
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template<typename F>
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using args_t = typename function_traits<std::remove_cvref_t<F>>::args;
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template<typename F>
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inline constexpr std::size_t arity_v = function_traits<std::remove_cvref_t<F>>::arity;
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// ── Tuple detection ───────────────────────────────────────────────────────────
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template<typename T>
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struct is_tuple : std::false_type {};
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template<typename... Ts>
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struct is_tuple<std::tuple<Ts...>> : std::true_type {};
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template<typename T>
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inline constexpr bool is_tuple_v = is_tuple<T>::value;
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// ── Normalise return type to always be a tuple ────────────────────────────────
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// void → std::tuple<>
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// T (non-tup) → std::tuple<T>
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// tuple<...> → tuple<...> (unchanged)
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template<typename T>
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struct normalise_return {
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using type = std::tuple<T>;
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};
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template<>
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struct normalise_return<void> {
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using type = std::tuple<>;
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};
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template<typename... Ts>
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struct normalise_return<std::tuple<Ts...>> {
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using type = std::tuple<Ts...>;
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};
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template<typename T>
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using normalised_return_t = typename normalise_return<T>::type;
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// ── Output count from a function type ────────────────────────────────────────
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template<typename F>
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inline constexpr std::size_t output_count_v =
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std::tuple_size_v<normalised_return_t<return_t<F>>>;
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} // namespace kpn
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