When function template is specialized in a different namespace, GCC and clang disagree

Question

See the following code:

namespace ns {

template <typename T>
void func() {}

}

template <>
void ns::func<int>() {}

int main() {}

While clang 3.6 (C++14) compiles fine, GCC 5.2 (C++14) throws the following error

main.cpp:9:20: error: specialization of 'template<class T> void ns::func()' in different namespace [-fpermissive]
 void ns::func<int>() {}
                    ^
main.cpp:4:6: error:   from definition of 'template<class T> void ns::func()' [-fpermissive]
 void func() {}
      ^

So, what does the standard say about this? Who is correct?

Answer 1

What does the Standard (n3797) say?

14.7.3    Explicit Specialization    [temp.expl.spec]

An explicit specialization shall be declared in a namespace enclosing the specialized template. An explicit specialization whose declarator-id is not qualified shall be declared in the nearest enclosing namespace of the template, or, if the namespace is inline (7.3.1), any namespace from its enclosing namespace set. Such a declaration may also be a definition. If the declaration is not a definition, the specialization may be defined later (7.3.1.2).

Verdict: Your specialization is an explicit specialization, and it is qualified, meaning that the snippet is legal. As such, the behavior shown by clang is the correct one.

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The relevant bug report for gcc:

• gcc.gnu.org/bugzilla - Bug 56480 - Explicit specialization in a namespace enclosing the specialized template