https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89596
Bug ID: 89596
Summary: [8 regression] Multiple templated conversion operators
result in compilation error
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: jleahy+gcc at gmail dot com
Target Milestone: ---
The follow code compiles fine on GCC <=7.4 (and also on Clang). However on 8.0
(and trunk) it fails.
template<typename T>
struct Bar {
Bar() = default;
Bar(double x) {}
};
struct Foo {
template<typename T>
operator T() {
return T();
}
template<typename T>
operator Bar<T>() {
return Bar<T>();
}
};
void test() {
(void)static_cast<Bar<int>>(Foo());
}
The following error is produced:
<source>: In function 'void test()':
<source>:20:38: error: call of overloaded 'Bar(Foo)' is ambiguous
(void)static_cast<Bar<int>>(Foo());
<source>:5:5: note: candidate: 'Bar<T>::Bar(double) [with T = int]'
Bar(double x) {}
<source>:3:8: note: candidate: 'constexpr Bar<int>::Bar(const Bar<int>&)'
struct Bar {
<source>:3:8: note: candidate: 'constexpr Bar<int>::Bar(Bar<int>&&)'
I believe from the standard GCC should consider all converting constructors (of
which there are none applicable) and user-defined conversion operators (of
which both are applicable) then apply normal overload resolution. During
overload resolution one of the two conversion operators will be discarded as
it's less specialized than the other.
