type_traits.h

/* *   Copyright (c) 2011-2017 Luke Benstead https://simulant-engine.appspot.com
 *
 *     This file is part of Simulant.
 *
 *     Simulant is free software: you can redistribute it and/or modify
 *     it under the terms of the GNU Lesser General Public License as published by
 *     the Free Software Foundation, either version 3 of the License, or
 *     (at your option) any later version.
 *
 *     Simulant 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 Lesser General Public License for more details.
 *
 *     You should have received a copy of the GNU Lesser General Public License
 *     along with Simulant.  If not, see <http://www.gnu.org/licenses/>.
 */
 
#ifndef CORE_TYPE_TRAITS_HPP
#define CORE_TYPE_TRAITS_HPP
 
#include <type_traits>
#include <utility>
 
namespace smlt {
inline namespace v1 {
 
/* custom type traits */
/* tuple_size is used by unpack, so we expect it to be available.
 * We also expect ::std::get<N> to be available for the give type T
 */
template <class T>
class is_unpackable {
  template <class U> using tuple_size_t = typename ::std::tuple_size<U>::type;
  template <class U> static void check (tuple_size_t<U>*) noexcept;
  template <class> static void check (...) noexcept(false);
public:
  static constexpr bool value = noexcept(check<T>(nullptr));
};
 
/* Used for types that have a .at(size_type) member function */
template <class T>
class is_runpackable {
  template <class U>
  static auto check (U* u) noexcept -> decltype(u->at(0ul), void());
  template <class> static void check (...) noexcept(false);
public:
  static constexpr bool value = noexcept(check<T>(nullptr));
};
 
/* extracts the class of a member function ponter */
template <class T> struct class_of { using type = T; };
template <class Signature, class Type>
struct class_of<Signature Type::*> { using type = Type; };
 
/* forward declaration */
template <class... Args> struct invokable;
template <class... Args> struct invoke_of;
template <class T> struct result_of; /* SFINAE result_of */
 
/* C++14 style aliases for standard traits */
template <class T>
using remove_volatile_t = typename ::std::remove_volatile<T>::type;
 
template <class T>
using remove_const_t = typename ::std::remove_const<T>::type;
template <class T> using remove_cv_t = typename ::std::remove_cv<T>::type;
 
template <class T>
using add_volatile_t = typename ::std::add_volatile<T>::type;
template <class T> using add_const_t = typename ::std::add_const<T>::type;
template <class T> using add_cv_t = typename ::std::add_cv<T>::type;
 
template <class T>
using add_lvalue_reference_t = typename ::std::add_lvalue_reference<T>::type;
 
template <class T>
using add_rvalue_reference_t = typename ::std::add_rvalue_reference<T>::type;
 
template <class T>
using remove_reference_t = typename ::std::remove_reference<T>::type;
 
template <class T>
using remove_pointer_t = typename ::std::remove_pointer<T>::type;
 
template <class T> using add_pointer_t = typename ::std::add_pointer<T>::type;
 
template <class T>
using make_unsigned_t = typename ::std::make_unsigned<T>::type;
template <class T> using make_signed_t = typename ::std::make_signed<T>::type;
 
template <class T>
using remove_extent_t = typename ::std::remove_extent<T>::type;
 
template <class T>
using remove_all_extents_t = typename ::std::remove_all_extents<T>::type;
 
template < ::std::size_t Len, ::std::size_t Align>
using aligned_storage_t = typename ::std::aligned_storage<Len, Align>::type;
 
template <class T> using decay_t = typename ::std::decay<T>::type;
 
template <bool B, class T = void>
using enable_if_t = typename ::std::enable_if<B, T>::type;
 
template <bool B, class T, class F>
using conditional_t = typename ::std::conditional<B, T, F>::type;
 
template <class T>
using underlying_type_t = typename ::std::underlying_type<T>::type;
 
/* custom type trait specializations */
template <class... Args> using invoke_of_t = typename invoke_of<Args...>::type;
template <class T> using class_of_t = typename class_of<T>::type;
 
namespace impl {
 
struct undefined { undefined (...); };
 
/* Get the result of an attempt at the INVOKE expression */
/* fallback */
template <class... Args> auto invoke_expr (undefined, Args&&...) -> undefined;
 
template <class Functor, class Object, class... Args>
auto invoke_expr (Functor&& fun, Object&& obj, Args&&... args) -> enable_if_t<
  ::std::is_member_function_pointer<remove_reference_t<Functor>>::value and
  ::std::is_base_of<
    class_of_t<remove_reference_t<Functor>>,
    remove_reference_t<Object>
  >::value,
  decltype((::std::forward<Object>(obj).*fun)(::std::forward<Args>(args)...))
>;
 
template <class Functor, class Object, class... Args>
auto invoke_expr (Functor&& fun, Object&& obj, Args&&... args) -> enable_if_t<
  ::std::is_member_function_pointer<remove_reference_t<Functor>>::value and
  not ::std::is_base_of<
    class_of_t<remove_reference_t<Functor>>,
    remove_reference_t<Object>
  >::value,
  decltype(
    ((*::std::forward<Object>(obj)).*fun)(::std::forward<Args>(args)...)
  )
>;
 
template <class Functor, class Object>
auto invoke_expr (Functor&& functor, Object&& object) -> enable_if_t<
  ::std::is_member_object_pointer<remove_reference_t<Functor>>::value and
  ::std::is_base_of<
    class_of_t<remove_reference_t<Functor>>,
    remove_reference_t<Object>
  >::value,
  decltype(::std::forward<Object>(object).*functor)
>;
 
template <class Functor, class Object>
auto invoke_expr (Functor&& functor, Object&& object) -> enable_if_t<
  ::std::is_member_object_pointer<remove_reference_t<Functor>>::value and
  not ::std::is_base_of<
    class_of_t<remove_reference_t<Functor>>,
    remove_reference_t<Object>
  >::value,
  decltype((*::std::forward<Object>(object)).*functor)
>;
 
template <class Functor, class... Args>
auto invoke_expr (Functor&& functor, Args&&... args) -> decltype(
  ::std::forward<Functor>(functor)(::std::forward<Args>(args)...)
);
 
template <bool, class... Args> struct invoke_of { };
template <class... Args>
struct invoke_of<true, Args...> {
  using type = decltype(invoke_expr(::std::declval<Args>()...));
};
 
/* swappable implementation details */
using ::std::declval;
using ::std::swap;
 
template <class T, class U>
class is_swappable {
  template <class X, class Y>
  static auto check (int) noexcept -> decltype(
    swap(declval<X&>(), declval<Y&>()),
    void()
  );
  template <class X, class Y> static void check (...) noexcept(false);
public:
  static constexpr bool value =
    noexcept(check<T, U>(0)) and noexcept(check<U, T>(0));
};
 
template <class T, class U>
struct is_nothrow_swappable : ::std::integral_constant<
  bool,
  is_swappable<T, U>::value and noexcept(swap(declval<T&>(), declval<U&>()))
> { };
 
} /* namespace impl */
 
template <class... Args> struct invokable : ::std::integral_constant<
  bool,
  not ::std::is_same<
    decltype(impl::invoke_expr(::std::declval<Args>()...)),
    impl::undefined
  >::value
> { };
 
template <class... Args> struct invoke_of :
  impl::invoke_of<invokable<Args...>::value, Args...>
{ };
 
template <class F, class... Args>
struct result_of<F(Args...)> : invoke_of<F, Args...> { };
 
template <class T> using result_of_t = typename result_of<T>::type;
 
template <class... Ts> struct common_type;
 
template <class T> struct common_type<T> { using type = decay_t<T>; };
template <class T, class U>
struct common_type<T, U> {
  using type = decay_t<
    decltype(true ? ::std::declval<T>() : ::std::declval<U>())
  >;
};
 
template <class T, class U, class... Ts>
struct common_type<T, U, Ts...> {
  using type = typename common_type<
    typename common_type<T, U>::type,
    Ts...
  >::type;
};
 
template <class... T> using common_type_t = typename common_type<T...>::type;
 
/* is_null_pointer */
template <class T> struct is_null_pointer : ::std::false_type { };
 
template <>
struct is_null_pointer<add_cv_t< ::std::nullptr_t>> : ::std::true_type { };
template <>
struct is_null_pointer< ::std::nullptr_t volatile> : ::std::true_type { };
template <>
struct is_null_pointer< ::std::nullptr_t const> : ::std::true_type { };
template <>
struct is_null_pointer< ::std::nullptr_t> : ::std::true_type { };
 
/* is_swappable */
template <class T, class U=T>
using is_swappable = ::std::integral_constant<
  bool,
  impl::is_swappable<T, U>::value
>;
 
/* is_nothrow_swappable */
template <class T, class U=T>
using is_nothrow_swappable = impl::is_nothrow_swappable<T, U>;
 
/* all-traits */
template <class...> struct all_traits;
template <class T, class... Args>
struct all_traits<T, Args...> : ::std::integral_constant<bool,
  T::value and all_traits<Args...>::value
> { };
template <> struct all_traits<> : ::std::true_type { };
 
/* any-traits */
template <class...> struct any_traits;
template <class T, class... Args>
struct any_traits<T, Args...> : ::std::integral_constant<bool,
  T::value or any_traits<Args...>::value
> { };
template <> struct any_traits<> : ::std::false_type { };
 
/* no-traits */
template <class... Args> struct no_traits : ::std::integral_constant<bool,
  not all_traits<Args...>::value
> { };
 
}} /* namespace core::v1 */
 
#endif /* CORE_TYPE_TRAITS_HPP */