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common_view
's converting constructor is bad, tooSection: 26.7.20.2 [range.common.view] Status: C++23 Submitter: Casey Carter Opened: 2020-02-20 Last modified: 2023-11-22
Priority: 0
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Discussion:
LWG 3280(i) struck the problematic/extraneous converting constructor templates from the
meow_view
range adaptor types in the standard library with the exception of common_view
.
The omission of common_view
seems to have been simply an oversight: its converting constructor
template is no less problematic or extraneous. We should remove common_view
's converting
constructor template as well to finish the task. Both cmcstl2
and range-v3
removed
the converting constructor template from common_view
when removing the other converting
constructor templates, so we have implementation experience that this change is good as well as
consistent with the general thrust of LWG 3280(i).
[2020-03-11 Issue Prioritization]
Status set to Tentatively Ready after seven positive votes on the reflector.
[2020-11-09 Approved In November virtual meeting. Status changed: Tentatively Ready → WP.]
Proposed resolution:
This wording is relative to N4849.
Modify 26.7.20.2 [range.common.view], class template common_view
synopsis, as indicated:
[…] constexpr explicit common_view(V r);[…]template<viewable_range R> requires (!common_range<R> && constructible_from<V, all_view<R>>) constexpr explicit common_view(R&& r);constexpr V base() const& requires copy_constructible<V> { return base_; } […]template<viewable_range R> requires (!common_range<R> && constructible_from<V, all_view<R>>) constexpr explicit common_view(R&& r);
-2- Effects: Initializesbase_
withviews::all(std::forward<R>(r))
.