This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 115f. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
2024-12-06
[Voted into WP at March, 2010 meeting.]
Consider the following example:
struct C { }; struct A { explicit operator int() const; explicit operator C() const; }; struct B { int i; B(const A& a): i(a) { } }; int main() { A a; int i = a; int j(a); C c = a; C c2(a); }
It's clear that the B constructor and the declaration of j are well-formed and the declarations of i and c are ill-formed. But what about the declaration of c2? This is supposed to work, but it doesn't under the current wording.
C c2(a) is direct-initialization of a class, so constructors are considered. The only possible candidate is the default copy constructor. So we look for a conversion from A to const C&. There is a conversion operator to C, but it is explicit and we are now performing copy-initialization of a reference temporary, so it is not a candidate, and the declaration of c2 is ill-formed.
Proposed resolution (October, 2009):
Change 12.2.2.5 [over.match.copy] paragraph 1 second bullet as follows: