poly_obj.h

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/* *****************************************************************************
 * kblib is a general utility library for C++14 and C++17, intended to provide
 * performant high-level abstractions and more expressive ways to do simple
 * things.
 *
 * Copyright (c) 2021 killerbee
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 * ****************************************************************************/
 
#ifndef POLY_OBJ_H
#define POLY_OBJ_H
 
#include "hash.h"
#include "variant.h"
 
namespace kblib {
 
enum class construct_type : unsigned {
   none = 0,
   copy_only = 1,
   move = 2,
   both = 3,
   throw_move = 4,
   both_throw = 5,
};
KBLIB_NODISCARD constexpr auto operator|(construct_type l,
                                         construct_type r) noexcept
    -> construct_type {
   return static_cast<construct_type>(etoi(l) | etoi(r));
}
 
KBLIB_NODISCARD constexpr auto operator&(construct_type l,
                                         construct_type r) noexcept
    -> construct_type {
   return static_cast<construct_type>(etoi(l) & etoi(r));
}
 
KBLIB_NODISCARD constexpr auto operator*(construct_type l, bool r) noexcept
    -> construct_type {
   return r ? l : construct_type::none;
}
 
namespace detail_poly {
 
   KBLIB_NODISCARD constexpr auto copyable(construct_type type) noexcept
       -> bool {
      return (type & construct_type::copy_only) != construct_type::none;
   }
   KBLIB_NODISCARD constexpr auto movable(construct_type type) noexcept
       -> bool {
      return (type & construct_type::move) != construct_type::none;
   }
   KBLIB_NODISCARD constexpr auto nothrow_movable(construct_type type) noexcept
       -> bool {
      return (type & construct_type::move) != construct_type::none
             and (type & construct_type::throw_move) == construct_type::none;
   }
 
   KBLIB_NODISCARD constexpr auto make_ctype(bool copyable, bool movable,
                                             bool nothrow_movable)
       -> construct_type {
      if (copyable) {
         if (not movable) {
            return construct_type::copy_only;
         } else if (nothrow_movable) {
            return construct_type::both;
         } else {
            return construct_type::both_throw;
         }
      } else if (movable) {
         return construct_type::move;
      } else {
         return construct_type::none;
      }
   }
 
   template <construct_type traits>
   struct construct_conditional;
 
   template <>
   struct construct_conditional<construct_type::none> {
      construct_conditional() noexcept = default;
      construct_conditional(const construct_conditional&) = delete;
      construct_conditional(construct_conditional&&) = delete;
 
      auto operator=(const construct_conditional&)
          -> construct_conditional& = default;
      auto operator=(construct_conditional&&)
          -> construct_conditional& = default;
      ~construct_conditional() = default;
   };
 
   template <>
   struct construct_conditional<construct_type::copy_only> {
      construct_conditional() noexcept = default;
      construct_conditional(const construct_conditional&) noexcept = default;
      construct_conditional(construct_conditional&&) = delete;
 
      auto operator=(const construct_conditional&)
          -> construct_conditional& = default;
      auto operator=(construct_conditional&&)
          -> construct_conditional& = default;
      ~construct_conditional() = default;
   };
 
   template <>
   struct construct_conditional<construct_type::move> {
      construct_conditional() noexcept = default;
      construct_conditional(const construct_conditional&) noexcept = delete;
      construct_conditional(construct_conditional&&) noexcept = default;
 
      auto operator=(const construct_conditional&)
          -> construct_conditional& = default;
      auto operator=(construct_conditional&&)
          -> construct_conditional& = default;
      ~construct_conditional() = default;
   };
 
   template <>
   struct construct_conditional<construct_type::both> {};
 
   template <>
   struct construct_conditional<construct_type::throw_move> {
      construct_conditional() noexcept = default;
      construct_conditional(const construct_conditional&) noexcept = delete;
      construct_conditional(construct_conditional&&) noexcept(false) {}
 
      auto operator=(const construct_conditional&)
          -> construct_conditional& = default;
      auto operator=(construct_conditional&&)
          -> construct_conditional& = default;
      ~construct_conditional() = default;
   };
 
   template <>
   struct construct_conditional<construct_type::both_throw> {
      construct_conditional() noexcept = default;
      construct_conditional(const construct_conditional&) = default;
      construct_conditional(construct_conditional&&) noexcept(false) {}
 
      auto operator=(const construct_conditional&)
          -> construct_conditional& = default;
      auto operator=(construct_conditional&&)
          -> construct_conditional& = default;
      ~construct_conditional() = default;
   };
 
   template <typename T>
   constexpr construct_type construct_traits
       = construct_type::copy_only* std::is_copy_constructible<T>::value
         | construct_type::move* std::is_move_constructible<T>::value
         | construct_type::throw_move*(
             std::is_move_constructible<T>::value
             & not std::is_nothrow_move_constructible<T>::value);
 
   template <typename T, typename hash = void>
   struct erased_hash_t {};
 
   template <typename T>
   struct erased_hash_t<T, void_t<fakestd::invoke_result_t<std::hash<T>, T>>> {
      static auto default_hash(void* obj) -> std::size_t {
         return std::hash<T>()(*static_cast<const T*>(obj));
      }
 
      alias<std::size_t (*)(void*)> hash = &default_hash;
   };
 
   template <typename T, typename hash = void>
   struct kblib_erased_hash_t {};
 
   template <typename T>
   struct kblib_erased_hash_t<
       T, void_t<fakestd::invoke_result_t<std::hash<T>, T>>> {
      static auto default_hash(void* obj) -> std::size_t {
         return FNV_hash<T>{}(*static_cast<const T*>(obj));
      }
 
      alias<std::size_t (*)(void*)> hash = &default_hash;
   };
 
   template <typename Traits>
   struct erased_construct
       : Traits::copy_t
       , Traits::move_t
       , Traits::destroy_t {
      using Traits::copy_t::copy;
      using Traits::move_t::move;
 
      using Traits::destroy_t::destroy;
   };
 
   template <typename T, typename Traits>
   KBLIB_NODISCARD auto make_ops_t() noexcept -> erased_construct<Traits> {
      static_assert(implies<Traits::copyable,
                            std::is_copy_constructible<T>::value>::value,
                    "T must be copy constructible if Traits is.");
      static_assert(
          implies<Traits::nothrow_movable,
                  std::is_nothrow_move_constructible<T>::value>::value,
          "T must be nothrow move constructible if Traits is.");
      static_assert(
          implies<Traits::movable, std::is_move_constructible<T>::value>::value,
          "T must be move constructible if Traits is.");
      return {{typename Traits::copy_t{static_cast<T*>(nullptr)}},
              {typename Traits::move_t{static_cast<T*>(nullptr)}},
              {typename Traits::destroy_t{static_cast<T*>(nullptr)}}};
   }
 
   template <typename T, typename = void>
   struct extract_derived_size
       : std::integral_constant<std::size_t, sizeof(T)> {};
   template <typename T>
   struct extract_derived_size<T, void_if_t<(T::max_derived_size > sizeof(T))>>
       : std::integral_constant<std::size_t, T::max_derived_size> {};
 
} // namespace detail_poly
 
template <typename T>
inline auto noop(void*, const T*) -> T* {
   return nullptr;
}
template <typename T, bool nothrow>
inline auto noop(void*, T*) noexcept(nothrow) -> T* {
   return nullptr;
}
template <typename Obj, bool copyable>
struct default_copy {
 private:
   template <typename T>
   static auto do_copy(void* dest, const Obj* from) -> Obj* {
      return static_cast<Obj*>(new (dest) T(*static_cast<const T*>(from)));
   }
 
   auto (*p_copy)(void* dest, const Obj* from) -> Obj* = &noop<Obj>;
 
 public:
   default_copy() noexcept = default;
   template <typename T>
   explicit default_copy(T*) noexcept
       : p_copy(&do_copy<T>) {}
 
   KBLIB_NODISCARD auto copy(void* dest, const Obj* from) -> Obj* {
      return p_copy(dest, from);
   }
};
template <typename Obj>
struct default_copy<Obj, false> {
   default_copy() noexcept = default;
   template <typename T>
   explicit default_copy(T*) noexcept {}
   auto copy(void* dest, const Obj* from) -> Obj* = delete;
};
template <typename Obj, auto (Obj::*clone)(void*) const->Obj*>
struct clone_copy {
   clone_copy() = default;
   template <typename T>
   clone_copy(T*) {}
 
   KBLIB_NODISCARD auto copy(void* dest, const Obj* from) -> Obj* {
      return (from->*clone)(dest);
   }
};
template <typename Obj, bool movable, bool nothrow, bool copyable>
struct default_move {
 private:
   template <typename T>
   static auto do_move(void* dest, Obj* from) noexcept(nothrow) -> Obj* {
      return static_cast<Obj*>(new (dest) T(std::move(*static_cast<T*>(from))));
   }
   // noexcept isn't working here on clang
   auto (*p_move)(void* dest, Obj* from) noexcept(false)
       -> Obj* = &noop<Obj, nothrow>;
 
 public:
   default_move() noexcept = default;
   template <typename T>
   explicit default_move(T*) noexcept
       : p_move(&do_move<T>) {}
 
   KBLIB_NODISCARD auto move(void* dest, Obj* from) noexcept(nothrow) -> Obj* {
      return p_move(dest, from);
   }
};
template <typename Obj, bool nothrow>
struct default_move<Obj, false, nothrow, false> {
   default_move() noexcept = default;
   template <typename T>
   explicit default_move(T*) noexcept {}
   auto move(void* dest, Obj* from) noexcept(nothrow) -> Obj* = delete;
};
// fallback on copy
template <typename Obj, bool nothrow>
struct default_move<Obj, false, nothrow, true>
    : private default_copy<Obj, true> {
   using default_copy<Obj, true>::default_copy;
 
   KBLIB_NODISCARD auto move(void* dest, const Obj* from) noexcept(nothrow)
       -> Obj* {
      return this->copy(dest, from);
   }
};
template <typename Obj>
struct default_destroy {
   default_destroy() noexcept = default;
   template <typename T>
   explicit default_destroy(T*) noexcept {}
 
   auto destroy(Obj* obj) -> void { obj->~Obj(); }
   static_assert(std::has_virtual_destructor<Obj>::value,
                 "Obj must have a virtual destructor");
};
 
// TODO(killerbee13): Distinguish between pointers to T and to
// most-derived-object
 
template <typename Obj,
          construct_type CType = detail_poly::construct_traits<Obj>>
struct poly_obj_traits {
 
   constexpr static std::size_t default_capacity
       = detail_poly::extract_derived_size<Obj>::value;
 
   constexpr static std::size_t alignment
       = std::max(alignof(Obj), alignof(std::max_align_t));
 
   constexpr static bool copyable = detail_poly::copyable(CType);
 
   constexpr static bool movable = detail_poly::movable(CType);
   constexpr static bool nothrow_movable = detail_poly::nothrow_movable(CType);
 
   using copy_t = default_copy<Obj, copyable>;
 
   using move_t = default_move<Obj, movable, nothrow_movable, copyable>;
 
   using destroy_t = default_destroy<Obj>;
   static_assert(std::is_empty<destroy_t>::value, "");
};
 
template <typename Obj>
using move_only_traits = poly_obj_traits<Obj, construct_type::move>;
template <typename Obj>
using no_move_traits = poly_obj_traits<Obj, construct_type::none>;
 
template <typename Obj, std::size_t Capacity = 0,
          typename Traits = poly_obj_traits<Obj>>
class poly_obj
    : private detail_poly::construct_conditional<detail_poly::make_ctype(
          Traits::copyable, Traits::movable, Traits::nothrow_movable)>
    , private detail_poly::erased_construct<Traits> {
 private:
   using disabler = detail_poly::construct_conditional<detail_poly::make_ctype(
       Traits::copyable, Traits::movable, Traits::nothrow_movable)>;
   using ops_t = detail_poly::erased_construct<Traits>;
 
 public:
   static constexpr std::size_t capacity
       = Capacity > 0 ? Capacity : Traits::default_capacity;
 
   static_assert(capacity >= sizeof(Obj),
                 "Capacity must be large enough for the object type.");
   static_assert(not std::is_array<Obj>::value,
                 "poly_obj of array type is disallowed.");
 
   using base_type = Obj;
   using traits_type = Traits;
 
 
   constexpr poly_obj() = default;
   constexpr poly_obj(std::nullptr_t) noexcept
       : poly_obj() {}
   constexpr poly_obj(const Obj& obj)
       : ptr(new (data) Obj(obj)) {}
   constexpr poly_obj(Obj&& obj) noexcept(Traits::nothrow_movable)
       : ptr(new (data) Obj(std::move(obj))) {}
 
   template <typename... Args,
             typename std::enable_if_t<
                 std::is_constructible<Obj, Args...>::value, int> = 0>
   constexpr explicit poly_obj(fakestd::in_place_t, Args&&... args) noexcept(
       std::is_nothrow_constructible<Obj, Args&&...>::value)
       : ops_t(detail_poly::make_ops_t<Obj, Traits>())
       , ptr(new (data) Obj(std::forward<Args>(args)...)) {}
 
   template <typename... Args,
             typename std::enable_if_t<
                 std::is_constructible<Obj, Args...>::value, int> = 0>
   constexpr explicit poly_obj(kblib::in_place_agg_t, Args&&... args) noexcept(
       std::is_nothrow_constructible<Obj, Args&&...>::value)
       : ops_t(detail_poly::make_ops_t<Obj, Traits>())
       , ptr(new (data) Obj{std::forward<Args>(args)...}) {}
 
   template <typename U, typename... Args>
   KBLIB_NODISCARD static auto make(Args&&... args) noexcept(
       std::is_nothrow_constructible<U, Args&&...>::value) -> poly_obj {
      static_assert(sizeof(U) <= capacity,
                    "U must fit inside of the inline capacity.");
      static_assert(alignof(U) <= Traits::alignment,
                    "U must be no more aligned than Traits::alignment");
      static_assert(std::is_base_of<Obj, U>::value
                        and std::is_convertible<U*, Obj*>::value,
                    "Obj must be an accessible base of Obj.");
      static_assert(
          implies<Traits::copyable,
                  std::is_copy_constructible<U>::value>::value,
          "U must be copy constructible if Traits::copyable is true.");
      static_assert(
          implies<Traits::movable, std::is_move_constructible<U>::value>::value,
          "U must be move constructible if Traits::movable is true.");
      return {tag<U>{}, std::forward<Args>(args)...};
   }
 
   template <typename U, typename... Args>
   KBLIB_NODISCARD static auto make_aggregate(Args&&... args) noexcept(
       std::is_nothrow_constructible<U, Args&&...>::value) -> poly_obj {
      static_assert(sizeof(U) <= capacity,
                    "U must fit inside of the inline capacity.");
      static_assert(alignof(U) <= Traits::alignment,
                    "U must be no more aligned than Traits::alignment");
      static_assert(std::is_base_of<Obj, U>::value
                        and std::is_convertible<U*, Obj*>::value,
                    "Obj must be an accessible base of Obj.");
      static_assert(
          implies<Traits::copyable,
                  std::is_copy_constructible<U>::value>::value,
          "U must be copy constructible if Traits::copyable is true.");
      static_assert(
          implies<Traits::movable, std::is_move_constructible<U>::value>::value,
          "U must be move constructible if Traits::movable is true.");
      return {tag<U, true>{}, std::forward<Args>(args)...};
   }
 
 
   constexpr poly_obj(const poly_obj& other)
       : disabler(other)
       , ops_t(other) {
      if (other.ptr) {
         ptr = this->copy(data, other.ptr);
      }
   }
   constexpr poly_obj(poly_obj&& other) noexcept(Traits::nothrow_movable)
       : disabler(std::move(other))
       , ops_t(std::move(other)) {
      if (other.ptr) {
         ptr = this->move(data, other.ptr);
      }
   }
 
   auto operator=(const poly_obj& other) & -> poly_obj& {
      if (this == &other) {
         return *this;
      }
      clear();
      static_cast<ops_t&>(*this) = other;
      if (other.ptr) {
         ptr = this->copy(data, other.ptr);
      }
      return *this;
   }
 
   auto operator=(poly_obj&& other) & noexcept(Traits::nothrow_movable)
       -> poly_obj& {
      if (this == &other) {
         return *this;
      }
      clear();
      static_cast<ops_t&>(*this) = other;
      if (other.ptr) {
         ptr = this->move(data, other.ptr);
      }
      return *this;
   }
 
   KBLIB_NODISCARD auto has_value() const& noexcept -> bool { return ptr; }
 
   explicit operator bool() const& noexcept { return has_value(); }
 
 
   auto clear() noexcept -> void {
      if (ptr) {
         this->destroy(ptr);
         ptr = nullptr;
      }
      static_cast<ops_t&>(*this) = {};
   }
 
   ~poly_obj() noexcept {
      if (ptr) {
         this->destroy(ptr);
      }
   }
 
 
   KBLIB_NODISCARD auto operator*() & noexcept -> Obj& { return *get(); }
   KBLIB_NODISCARD auto operator*() const& noexcept -> const Obj& {
      return *get();
   }
   KBLIB_NODISCARD auto operator*() && noexcept(Traits::nothrow_movable)
       -> Obj&& {
      return std::move(*get());
   }
   KBLIB_NODISCARD auto operator*() const&& noexcept(Traits::nothrow_movable)
       -> const Obj&& {
      return std::move(*get());
   }
 
   KBLIB_NODISCARD auto get() & noexcept -> Obj* { return ptr; }
   KBLIB_NODISCARD auto get() const& noexcept -> const Obj* { return ptr; }
 
   KBLIB_NODISCARD auto operator->() & noexcept -> Obj* { return ptr; }
   KBLIB_NODISCARD auto operator->() const& noexcept -> const Obj* {
      return ptr;
   }
 
   template <typename... Args>
   auto operator()(Args&&... args) noexcept(
       is_nothrow_invocable<Obj&, Args&&...>::value)
       -> fakestd::invoke_result_t<Obj&, Args&&...> {
      return kblib::invoke(*get(), std::forward<Args>(args)...);
   }
   template <typename... Args>
   auto operator()(Args&&... args) const
       noexcept(is_nothrow_invocable<const Obj&, Args&&...>::value)
           -> fakestd::invoke_result_t<const Obj&, Args&&...> {
      return kblib::invoke(*get(), std::forward<Args>(args)...);
   }
 
   template <typename member_type>
   enable_if_t<not std::is_member_function_pointer<member_type Obj::*>::value,
               member_type>&
   operator->*(member_type Obj::*member) & noexcept {
      return get()->*member;
   }
 
   template <typename member_type>
   const enable_if_t<
       not std::is_member_function_pointer<member_type Obj::*>::value,
       member_type>&
   operator->*(member_type Obj::*member) const& noexcept {
      return get()->*member;
   }
 
   template <typename member_type>
   enable_if_t<not std::is_member_function_pointer<member_type Obj::*>::value,
               member_type>&&
   operator->*(member_type Obj::*member) && noexcept {
      return std::move(get()->*member);
   }
 
   template <typename member_type>
   const enable_if_t<
       not std::is_member_function_pointer<member_type Obj::*>::value,
       member_type>&&
   operator->*(member_type Obj::*member) const&& noexcept {
      return std::move(get()->*member);
   }
 
   template <typename member_type, typename... Args>
   KBLIB_NODISCARD auto operator->*(
       member_type (Obj::*member)(Args...)) & noexcept {
      return [member, value = get()](Args... args) -> decltype(auto) {
         return (value->*member)(std::forward<Args>(args)...);
      };
   }
 
   template <typename member_type, typename... Args>
   KBLIB_NODISCARD auto operator->*(member_type (Obj::*member)(Args...)
                                        const) & noexcept {
      return [member, value = get()](Args... args) -> decltype(auto) {
         return (value->*member)(std::forward<Args>(args)...);
      };
   }
 
   template <typename member_type, typename... Args>
   KBLIB_NODISCARD auto operator->*(member_type (Obj::*member)(Args...)
                                        const) const& noexcept {
      return [member, value = get()](Args... args) -> decltype(auto) {
         return (value->*member)(std::forward<Args>(args)...);
      };
   }
 
   template <typename member_type, typename... Args>
   KBLIB_NODISCARD auto operator->*(member_type (Obj::*member)(Args...)
                                        const) && noexcept {
      return [member, value = get()](Args... args) -> decltype(auto) {
         return (value->*member)(std::forward<Args>(args)...);
      };
   }
 
   template <typename member_type, typename... Args>
   KBLIB_NODISCARD auto operator->*(
       member_type (Obj::*member)(Args...) &) & noexcept {
      return [member, value = get()](Args... args) -> decltype(auto) {
         return (value->*member)(std::forward<Args>(args)...);
      };
   }
 
   template <typename member_type, typename... Args>
   KBLIB_NODISCARD auto operator->*(member_type (Obj::*member)(Args...)
                                        const&) & noexcept {
      return [member, value = get()](Args... args) -> decltype(auto) {
         return (value->*member)(std::forward<Args>(args)...);
      };
   }
 
   template <typename member_type, typename... Args>
   KBLIB_NODISCARD auto operator->*(member_type (Obj::*member)(Args...)
                                        const&) const& noexcept {
      return [member, value = get()](Args... args) -> decltype(auto) {
         return (value->*member)(std::forward<Args>(args)...);
      };
   }
 
   template <typename member_type, typename... Args>
   KBLIB_NODISCARD auto operator->*(member_type (Obj::*member)(Args...)
                                    &&) && noexcept {
      return [member, value = get()](Args... args) -> decltype(auto) {
         return (std::move(*value).*member)(std::forward<Args>(args)...);
      };
   }
 
   template <typename member_type, typename... Args>
   KBLIB_NODISCARD auto operator->*(member_type (Obj::*member)(Args...)
                                        const&) && noexcept {
      return [member, value = get()](Args... args) -> decltype(auto) {
         return (value->*member)(std::forward<Args>(args)...);
      };
   }
 
   template <typename member_type, typename... Args>
   KBLIB_NODISCARD auto operator->*(
       member_type (Obj::*member)(Args...)) && noexcept {
      return [member, value = get()](Args... args) -> decltype(auto) {
         return (value->*member)(std::forward<Args>(args)...);
      };
   }
 
   template <typename member_type, typename... Args>
   KBLIB_NODISCARD auto operator->*(member_type (Obj::*member)(Args...)
                                        const&&) && noexcept {
      return [member, value = get()](Args... args) -> decltype(auto) {
         return (std::move(*value).*member)(std::forward<Args>(args)...);
      };
   }
 
   template <typename member_type, typename... Args>
   KBLIB_NODISCARD auto operator->*(member_type (Obj::*member)(Args...)
                                        const&&) const&& noexcept {
      return [member, value = get()](Args... args) -> decltype(auto) {
         return (std::move(*value).*member)(std::forward<Args>(args)...);
      };
   }
 
 private:
   alignas(Traits::alignment) byte data[capacity]{};
   Obj* ptr{};
 
   template <typename U, bool = false>
   struct tag {};
 
   template <typename U, typename... Args>
   poly_obj(tag<U>, Args&&... args) noexcept(
       std::is_nothrow_constructible<U, Args&&...>::value)
       : ops_t(detail_poly::make_ops_t<U, Traits>())
       , ptr(new (data) U(std::forward<Args>(args)...)) {}
 
   template <typename U, typename... Args>
   poly_obj(tag<U, true>, Args&&... args) noexcept(
       std::is_nothrow_constructible<U, Args&&...>::value)
       : ops_t(detail_poly::make_ops_t<U, Traits>())
       , ptr(new (data) U{std::forward<Args>(args)...}) {}
};
 
template <bool warn>
constexpr auto poly_warn_if() -> std::nullptr_t {
   return {};
}
template <>
[[deprecated(
    "make_poly_obj<T, D, Capacity>(): Specifying capacity with this "
    "API is error-prone, consider "
    "using a type alias instead to avoid repetition.")]] constexpr inline auto
poly_warn_if<true>() -> std::nullptr_t {
   return {};
}
 
template <typename T, typename D = T, std::size_t Capacity = sizeof(D),
          typename Traits = poly_obj_traits<T>, typename... Args>
KBLIB_NODISCARD auto make_poly_obj(
    Args&&... args,
    std::nullptr_t = poly_warn_if<(Capacity != sizeof(D)
                                   and Capacity > Traits::default_capacity)>())
    -> poly_obj<T, std::max(Capacity, Traits::default_capacity), Traits> {
   return poly_obj<T, std::max(Capacity, Traits::default_capacity),
                   Traits>::template make<D>(std::forward<Args>(args)...);
}
 
} // namespace kblib
 
#endif // POLY_OBJ_H