diff options
Diffstat (limited to 'include/pybind11/detail/type_caster_base.h')
| -rw-r--r-- | include/pybind11/detail/type_caster_base.h | 203 |
1 files changed, 179 insertions, 24 deletions
diff --git a/include/pybind11/detail/type_caster_base.h b/include/pybind11/detail/type_caster_base.h index 8f3d0f37..16387506 100644 --- a/include/pybind11/detail/type_caster_base.h +++ b/include/pybind11/detail/type_caster_base.h @@ -822,26 +822,179 @@ using movable_cast_op_type typename std::add_rvalue_reference<intrinsic_t<T>>::type, typename std::add_lvalue_reference<intrinsic_t<T>>::type>>; -// std::is_copy_constructible isn't quite enough: it lets std::vector<T> (and similar) through when -// T is non-copyable, but code containing such a copy constructor fails to actually compile. -template <typename T, typename SFINAE = void> -struct is_copy_constructible : std::is_copy_constructible<T> {}; +// Does the container have a mapped type and is it recursive? +// Implemented by specializations below. +template <typename Container, typename SFINAE = void> +struct container_mapped_type_traits { + static constexpr bool has_mapped_type = false; + static constexpr bool has_recursive_mapped_type = false; +}; + +template <typename Container> +struct container_mapped_type_traits< + Container, + typename std::enable_if< + std::is_same<typename Container::mapped_type, Container>::value>::type> { + static constexpr bool has_mapped_type = true; + static constexpr bool has_recursive_mapped_type = true; +}; + +template <typename Container> +struct container_mapped_type_traits< + Container, + typename std::enable_if< + negation<std::is_same<typename Container::mapped_type, Container>>::value>::type> { + static constexpr bool has_mapped_type = true; + static constexpr bool has_recursive_mapped_type = false; +}; + +// Does the container have a value type and is it recursive? +// Implemented by specializations below. +template <typename Container, typename SFINAE = void> +struct container_value_type_traits : std::false_type { + static constexpr bool has_value_type = false; + static constexpr bool has_recursive_value_type = false; +}; + +template <typename Container> +struct container_value_type_traits< + Container, + typename std::enable_if< + std::is_same<typename Container::value_type, Container>::value>::type> { + static constexpr bool has_value_type = true; + static constexpr bool has_recursive_value_type = true; +}; + +template <typename Container> +struct container_value_type_traits< + Container, + typename std::enable_if< + negation<std::is_same<typename Container::value_type, Container>>::value>::type> { + static constexpr bool has_value_type = true; + static constexpr bool has_recursive_value_type = false; +}; + +/* + * Tag to be used for representing the bottom of recursively defined types. + * Define this tag so we don't have to use void. + */ +struct recursive_bottom {}; + +/* + * Implementation detail of `recursive_container_traits` below. + * `T` is the `value_type` of the container, which might need to be modified to + * avoid recursive types and const types. + */ +template <typename T, bool is_this_a_map> +struct impl_type_to_check_recursively { + /* + * If the container is recursive, then no further recursion should be done. + */ + using if_recursive = recursive_bottom; + /* + * Otherwise yield `T` unchanged. + */ + using if_not_recursive = T; +}; + +/* + * For pairs - only as value type of a map -, the first type should remove the `const`. + * Also, if the map is recursive, then the recursive checking should consider + * the first type only. + */ +template <typename A, typename B> +struct impl_type_to_check_recursively<std::pair<A, B>, /* is_this_a_map = */ true> { + using if_recursive = typename std::remove_const<A>::type; + using if_not_recursive = std::pair<typename std::remove_const<A>::type, B>; +}; -template <typename T, typename SFINAE = void> -struct is_move_constructible : std::is_move_constructible<T> {}; +/* + * Implementation of `recursive_container_traits` below. + */ +template <typename Container, typename SFINAE = void> +struct impl_recursive_container_traits { + using type_to_check_recursively = recursive_bottom; +}; -// Specialization for types that appear to be copy constructible but also look like stl containers -// (we specifically check for: has `value_type` and `reference` with `reference = value_type&`): if -// so, copy constructability depends on whether the value_type is copy constructible. template <typename Container> -struct is_copy_constructible< +struct impl_recursive_container_traits< Container, - enable_if_t< - all_of<std::is_copy_constructible<Container>, - std::is_same<typename Container::value_type &, typename Container::reference>, - // Avoid infinite recursion - negation<std::is_same<Container, typename Container::value_type>>>::value>> - : is_copy_constructible<typename Container::value_type> {}; + typename std::enable_if<container_value_type_traits<Container>::has_value_type>::type> { + static constexpr bool is_recursive + = container_mapped_type_traits<Container>::has_recursive_mapped_type + || container_value_type_traits<Container>::has_recursive_value_type; + /* + * This member dictates which type Pybind11 should check recursively in traits + * such as `is_move_constructible`, `is_copy_constructible`, `is_move_assignable`, ... + * Direct access to `value_type` should be avoided: + * 1. `value_type` might recursively contain the type again + * 2. `value_type` of STL map types is `std::pair<A const, B>`, the `const` + * should be removed. + * + */ + using type_to_check_recursively = typename std::conditional< + is_recursive, + typename impl_type_to_check_recursively< + typename Container::value_type, + container_mapped_type_traits<Container>::has_mapped_type>::if_recursive, + typename impl_type_to_check_recursively< + typename Container::value_type, + container_mapped_type_traits<Container>::has_mapped_type>::if_not_recursive>::type; +}; + +/* + * This trait defines the `type_to_check_recursively` which is needed to properly + * handle recursively defined traits such as `is_move_constructible` without going + * into an infinite recursion. + * Should be used instead of directly accessing the `value_type`. + * It cancels the recursion by returning the `recursive_bottom` tag. + * + * The default definition of `type_to_check_recursively` is as follows: + * + * 1. By default, it is `recursive_bottom`, so that the recursion is canceled. + * 2. If the type is non-recursive and defines a `value_type`, then the `value_type` is used. + * If the `value_type` is a pair and a `mapped_type` is defined, + * then the `const` is removed from the first type. + * 3. If the type is recursive and `value_type` is not a pair, then `recursive_bottom` is returned. + * 4. If the type is recursive and `value_type` is a pair and a `mapped_type` is defined, + * then `const` is removed from the first type and the first type is returned. + * + * This behavior can be extended by the user as seen in test_stl_binders.cpp. + * + * This struct is exactly the same as impl_recursive_container_traits. + * The duplication achieves that user-defined specializations don't compete + * with internal specializations, but take precedence. + */ +template <typename Container, typename SFINAE = void> +struct recursive_container_traits : impl_recursive_container_traits<Container> {}; + +template <typename T> +struct is_move_constructible + : all_of<std::is_move_constructible<T>, + is_move_constructible< + typename recursive_container_traits<T>::type_to_check_recursively>> {}; + +template <> +struct is_move_constructible<recursive_bottom> : std::true_type {}; + +// Likewise for std::pair +// (after C++17 it is mandatory that the move constructor not exist when the two types aren't +// themselves move constructible, but this can not be relied upon when T1 or T2 are themselves +// containers). +template <typename T1, typename T2> +struct is_move_constructible<std::pair<T1, T2>> + : all_of<is_move_constructible<T1>, is_move_constructible<T2>> {}; + +// std::is_copy_constructible isn't quite enough: it lets std::vector<T> (and similar) through when +// T is non-copyable, but code containing such a copy constructor fails to actually compile. +template <typename T> +struct is_copy_constructible + : all_of<std::is_copy_constructible<T>, + is_copy_constructible< + typename recursive_container_traits<T>::type_to_check_recursively>> {}; + +template <> +struct is_copy_constructible<recursive_bottom> : std::true_type {}; // Likewise for std::pair // (after C++17 it is mandatory that the copy constructor not exist when the two types aren't @@ -852,14 +1005,16 @@ struct is_copy_constructible<std::pair<T1, T2>> : all_of<is_copy_constructible<T1>, is_copy_constructible<T2>> {}; // The same problems arise with std::is_copy_assignable, so we use the same workaround. -template <typename T, typename SFINAE = void> -struct is_copy_assignable : std::is_copy_assignable<T> {}; -template <typename Container> -struct is_copy_assignable<Container, - enable_if_t<all_of<std::is_copy_assignable<Container>, - std::is_same<typename Container::value_type &, - typename Container::reference>>::value>> - : is_copy_assignable<typename Container::value_type> {}; +template <typename T> +struct is_copy_assignable + : all_of< + std::is_copy_assignable<T>, + is_copy_assignable<typename recursive_container_traits<T>::type_to_check_recursively>> { +}; + +template <> +struct is_copy_assignable<recursive_bottom> : std::true_type {}; + template <typename T1, typename T2> struct is_copy_assignable<std::pair<T1, T2>> : all_of<is_copy_assignable<T1>, is_copy_assignable<T2>> {}; |