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Combine partial_range template constructors

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Add an explicit check for rvalue ranges that own their storage, and then
allow any other rvalue input.
This commit is contained in:
Kp 2021-06-28 03:37:50 +00:00
parent 028f4f8a56
commit 3466a6f818
1 changed files with 21 additions and 6 deletions
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27
common/include/partial_range.h
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@ -119,14 +119,29 @@ public:
partial_range_t(partial_range_t &&) = default;
partial_range_t &operator=(const partial_range_t &) = default;
template <typename T>
partial_range_t(T &t) :
partial_range_t(T &&t) :
m_begin(partial_range_detail::adl_begin(t)), m_end(partial_range_detail::adl_end(t))
{
}
template <typename T>
partial_range_t(partial_range_t<T> &&t) :
m_begin(t.begin()), m_end(t.end())
{
/* If `T &&`, after reference collapsing, is an lvalue
* reference, then the object referenced by `t` will remain in
* scope after the statement that called this constructor, and
* there is no need to check whether the object `t` owns the
* iterated range.
*
* Otherwise, if `t` is an rvalue reference, assert that `t` is
* a view onto a range, rather than owning the range. A `t`
* that owns the storage would leave the iterators dangling.
*
* These checks are not precise. It is possible to have a type
* T that remains in scope, but frees its storage early, and
* leaves the range dangling. It is possible to have a type T
* that owns the storage, and is not destroyed after the
* containing statement terminates. Neither are good designs,
* and neither can be handled here. These checks attempt to
* catch obvious mistakes.
*/
if constexpr (!std::is_lvalue_reference<T &&>::value)
static_assert(!T::range_owns_iterated_storage::value, "rvalue reference to range requires that the range is a view, not an owner");
}
__attribute_warn_unused_result
iterator begin() const { return m_begin; }