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Section: 26.4.5 [range.refinements] Status: C++20 Submitter: Casey Carter Opened: 2020-01-25 Last modified: 2021-02-25
Priority: 0
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Discussion:
The definition of the contiguous_range concept in 26.4.5 [range.refinements]/2 requires that ranges::data(r) be valid for a contiguous_range r, but fails to impose the obvious semantic requirement that to_address(ranges::begin(r)) == ranges::data(r). In other words, data and begin must agree so that [begin(r), end(r)) and the counted range data(r) + [0, size(r)) (this is the new "counted range" specification syntax per working draft issue 2932) denote the same sequence of elements.
[2020-02 Prioritized as IMMEDIATE Monday morning in Prague]
Proposed resolution:
This wording is relative to N4849.
Modify 26.4.5 [range.refinements] as indicated:
-2- contiguous_range additionally requires that the ranges::data customization point (26.3.13 [range.prim.data]) is usable with the range.
template<class T> concept contiguous_range = random_access_range<T> && contiguous_iterator<iterator_t<T>> && requires(T& t) { { ranges::data(t) } -> same_as<add_pointer_t<range_reference_t<T>>>; };-?- Given an expression t such that decltype((t)) is T&, T models contiguous_range only if (to_address(ranges::begin(t)) == ranges::data(t)).
-3- The common_range concept […]