http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55663
Bug #: 55663
Summary: [C++11] Alias template combined with constexpr
function is considered non-const
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: daniel.krueg...@googlemail.com
Using gcc 4.8.0 20121209 (experimental) and compile with flags
-Wall -std=c++11 -pedantic
rejects the following program:
//-------------------------------
template<bool, class>
struct enable_if {};
template<class T>
struct enable_if<true, T> { using type = T; };
template<bool C, class T>
using req = typename enable_if<C, T>::type;
template<class T>
constexpr bool always() { return true; }
template<class T>
typename enable_if<always<T>(), void>::type
foo1(T){}
template<class T>
req<always<T>(), void>
foo2(T){}
int main() {
foo1(0); // OK
foo2(0); // Error #23
}
//-------------------------------
the diagnostics being:
"main.cpp||In function 'int main()':|
main.cpp|23|error: no matching function for call to 'foo2(int)'|
main.cpp|23|note: candidate is:|
main.cpp|19|note: template<class T> req<always<T>(), void> foo2(T)|
main.cpp|19|note: template argument deduction/substitution failed:|
main.cpp|19| required by substitution of 'template<class T> req<always<T>(),
void> foo2(T) [with T = int]'|
main.cpp|23|required from here|
main.cpp|19|error: integral expression 'always<int>()' is not constant|
main.cpp|19|error: trying to instantiate 'template<bool C, class T> using req
= typename enable_if::type'|
"
I found some similarity to bug 54648 but I'm not 100% sure whether this is a
dub
