https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66671
Bug ID: 66671
Summary: Failure to create a new family of templates for
template alias
Product: gcc
Version: 5.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: thiago at kde dot org
Target Milestone: ---
Whenever you use:
template <typename T>
using Z = Y<T>;
The template Z is different from Y and should be encoded separately. This can
be seen in the example:
====
#include <iostream>
template <template <typename> class>
struct X {
X() { std::cout << "1"; }
};
template <typename>
struct Y {};
template <typename T>
using Z = Y<T>;
template <>
struct X<Y> {
X() { std::cout << "2"; }
};
int main() {
X<Y> x1;
X<Z> x2;
}
====
(from: http://cppquiz.org/quiz/giveup/117)
With GCC 5.1.1, the above prints "22", whereas it prints "21" with ICC 16,
Clang 3.7 and MSVC 2013. The explanation from the quiz site is given as:
> According to §14.5.7¶1 in the standard, a template alias declaration
> resolve to a new family of types. The specialization cannot be used,
> and the first template delcaration is used instead, printing 1.
Disassembly with -O2 -fno-inline shows that Clang and ICC both call different
template specialisations of template class X:
leaq 16(%rsp), %rdi
callq _ZN1XI1YEC2Ev ; X<Y>::X()
leaq 8(%rsp), %rdi
callq _ZN1XI1ZEC2Ev ; X<Z>::X()
PS: should X<Z> count as a local type or a global one?
