https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66893
Bug ID: 66893
Summary: disallowed initialization of reference with
user-defined conversion function
Product: gcc
Version: 5.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: barry.revzin at gmail dot com
Target Milestone: ---
Consider the following:
struct B {};
struct S { explicit operator B(); };
int main() {
B const &t(S{});
}
According to [over.match.ref]:
Those non-explicit conversion
functions that are not hidden within S and yield type “lvalue reference to cv2
T2” (when initializing an lvalue reference or an rvalue reference to function)
or “cv2 T2” or “rvalue reference to cv2 T2” (when initializing an rvalue
reference or an lvalue reference to function), where “cv1 T” is
reference-compatible (8.5.3) with “cv2 T2”, are candidate functions.
In this case, B const (cv1 T) is reference-compatible with B (cv2 T2), so the
operator should be a candidate function. However, gcc rejects it:
main.cpp: In function 'int main()':
main.cpp:5:19: error: invalid initialization of reference of type 'const B&'
from expression of type 'S'
B const &t(S{});
^
