Is it C++ standard-compliant to define a variable using `A<int>::template B<int> x;`?
c++, c++11, compiler-construction, portability, templates
Solution
Even though it is a non-normative note, I think an answer can be given by n3797[temp.names]/6
As is the case with the `typename` prefix, the `template` prefix is allowed in cases where it is not strictly necessary; i.e., when the nested-name-specifier or the expression on the left of the `->` or `.` is not dependent on a template-parameter, or the use does not appear in the scope of a template.
In the OP's example, the prefix `template` is used outside the scope of a template, and the preceding nested-name-specifier is not dependent. Therefore, the prefix `template` is not required, but allowed here.
[expr.prim.general]/8
qualified-id: nested-name-specifier `template`opt unqualified-id
Plus [temp.names]/5
A name prefixed by the keyword `template` shall be a template-id or the name shall refer to a class template.
[temp.names]/1 says that `B<int>` is indeed a (simple-)template-id.
Problem
The following code is accepted by gcc, vc++, and clang. ``` template<class T> struct A { template<class U> struct B {}; }; int main() { A<int>::B<int> y; // OK as expected A<int>::template B<int> x; // Also OK! Is this standard-compliant? }; ``` Is it C++ standard-compliant to define a variable using `A<int>::template B<int> x;`?