This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of WP status.
Section: 18.4.4 [concept.convertible] Status: WP Submitter: Tim Song Opened: 2020-07-03 Last modified: 2020-11-09
Priority: 0
View other active issues in [concept.convertible].
View all other issues in [concept.convertible].
View all issues with WP status.
Discussion:
There are no expressions of type cv-qualified void because any such expression must be prvalues and 7.2.2 [expr.type]/2 states:
If a prvalue initially has the type "cv T", where T is a cv-unqualified non-class, non-array type, the type of the expression is adjusted to T prior to any further analysis.
However, 18.4.4 [concept.convertible] p1 states:
Given types From and To and an expression E such that decltype((E)) is add_rvalue_reference_t<From>, convertible_to<From, To> requires E to be both implicitly and explicitly convertible to type To.
When From is cv-qualified void, E does not exist, yet we do want convertible_to<const void, void> to be modeled.
[2020-07-12; Reflector prioritization]
Set priority to 0 and status to Tentatively Ready after five votes in favour during reflector discussions.
[2020-11-09 Approved In November virtual meeting. Status changed: Tentatively Ready → WP.]
Proposed resolution:
This wording is relative to N4861.
Modify 18.4.4 [concept.convertible] as indicated:
-1- Given types From and To and an expression E
such that decltype((E)) is add_rvalue_reference_t<From>whose type and value category are the same as those of declval<From>(), convertible_to<From, To> requires E to be both implicitly and explicitly convertible to type To. The implicit and explicit conversions are required to produce equal results.