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Flatten type hierarchy for enumerated_iterator

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Pass adjust_iterator_dereference_type directly, instead of passing
iterator_dereference_type and letting enumerated_iterator compute
adjust_iterator_dereference_type.
This commit is contained in:
Kp 2022-02-19 14:52:17 +00:00
parent f38a1b95a1
commit b1278b8e39
2 changed files with 19 additions and 3 deletions
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10
common/main/d_enumerate.h
View file

@ -59,12 +59,11 @@ typename std::remove_reference<typename std::remove_reference<T>::type::index_ty
}
template <typename range_index_type, typename range_iterator_type, typename iterator_dereference_type>
template <typename range_index_type, typename range_iterator_type, typename adjust_iterator_dereference_type>
class enumerated_iterator
{
range_iterator_type m_iter;
range_index_type m_idx;
using adjust_iterator_dereference_type = d_enumerate::detail::adjust_iterator_dereference_type<range_index_type, iterator_dereference_type>;
public:
using index_type = range_index_type;
using iterator_category = std::forward_iterator_tag;
@ -117,7 +116,7 @@ class enumerate : partial_range_t<range_iterator_type, range_index_type>
using enumerated_iterator_type = enumerated_iterator<
range_index_type,
range_iterator_type,
typename std::remove_cv<iterator_dereference_type>::type>;
d_enumerate::detail::adjust_iterator_dereference_type<range_index_type, typename std::remove_cv<iterator_dereference_type>::type>>;
const range_index_type m_idx;
public:
using range_owns_iterated_storage = std::false_type;
@ -130,6 +129,11 @@ public:
enumerate(range_type &&t, const index_type i = index_type{}) :
base_type(std::forward<range_type>(t)), m_idx(i)
{
/* Block using `enumerate` on an ephemeral range, since the storage
* owned by the range must exist until the `enumerate` object is
* fully consumed. If `range_type &&` is an ephemeral range, then its
* storage may cease to exist after this constructor returns.
*/
static_assert(!any_ephemeral_range<range_type &&>::value, "cannot enumerate storage of ephemeral ranges");
static_assert(std::is_rvalue_reference<range_type &&>::value || std::is_lvalue_reference<iterator_dereference_type>::value, "lvalue range must produce lvalue reference enumerated_value");
}

12
common/main/ephemeral_range.h
View file

@ -10,13 +10,25 @@
namespace detail {
/* In the general case, a range is ephemeral if `T` is an rvalue reference,
* since an rvalue may be moved or destroyed by the end of the statement.
*/
template <typename T>
std::is_rvalue_reference<T> is_ephemeral_range(...);
/* As a special exception to the general case, if the type T defines an inner
* type `range_owns_iterated_storage`, delegate the test to that type. This
* allows a type T to declare that it is only a view on longer-lived storage,
* and therefore the storage is not ephemeral even when `T` is an rvalue
* reference.
*/
template <typename T>
typename std::remove_reference<T>::type::range_owns_iterated_storage is_ephemeral_range(std::nullptr_t);
}
/* Define a convenience helper that applies the `is_ephemeral_range` test to
* any number of types.
*/
template <typename... Tn>
using any_ephemeral_range = std::disjunction<decltype(detail::is_ephemeral_range<Tn>(nullptr))...>;