Section: 26.4.4 [range.view] Status: Tentatively NAD Submitter: Hewill Kang Opened: 2023-08-22 Last modified: 2023-10-30 16:39:42 UTC
Priority: Not Prioritized
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Discussion:
Currently, the wording of is-derived-from-view-interface only detects whether type T is unambiguously derived from one base class view_interface<U> where U is not required to be T, which is not the intention of CRTP.
[2023-10-30; Reflector poll]
Set status to Tentatively NAD.
The wording correctly handles the case where T derives from Base
which derives from view_interface<Base>
.
We don't want it to only be satisfied for direct inheritance from
view_interface<T>
, but from any specialization of
view_interface
.
Previously the concept only checked for inheritance from view_base
but it was changed when view_interface
stopped inheriting from
view_base
.
Proposed resolution:
This wording is relative to N4958.
Modify 26.4.4 [range.view] as indicated:
template<class T> constexpr bool is-derived-from-view-interface = see below; // exposition only template<class T> constexpr bool enable_view = derived_from<T, view_base> || is-derived-from-view-interface<T>;-6- For a type T, is-derived-from-view-interface<T> is true if and only if T has exactly one public base class view_interface<T
U>for some type Uand T has no base classes of type view_interface<UV> for any other type UV.