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Section: 99 [concept.transform] Status: NAD Concepts Submitter: Daniel Krügler Opened: 2009-05-28 Last modified: 2016-01-28
Priority: Not Prioritized
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Discussion:
A recent news group article points to several defects in the specification of reference-related concepts.
One problem of the concept RvalueOf as currently defined in
99 [concept.transform]:
concept RvalueOf<typename T> {
typename type = T&&;
requires ExplicitlyConvertible<T&,type> && Convertible<T&&,type>;
}
template<typename T> concept_map RvalueOf<T&> {
typedef T&& type;
}
is that if T is an lvalue-reference, the requirement
Convertible<T&&,type> isn't satisfied for
lvalue-references, because after reference-collapsing in the concept
definition we have Convertible<T&,type> in this case,
which isn't satisfied in the concept map template and also is not the
right constraint either. I think that the reporter is right that
SameType requirements should do the job and that we also should
use the new RvalueReference concept to specify a best matching
type requirement.
Proposed resolution:
In 99 [concept.transform] before p. 4 change as indicated:
auto concept RvalueOf<typename T> {
typenameRvalueReference type = T&&;
requires ExplicitlyConvertible<T&, type> && Convertible<T&&, type>SameType<T&, type&>;
}