My compiler allows "T&...". Is this an extension?

Question

I was surprised when the following worked

template<typename T>
void f(T &...);

I thought that I have to declare "T" as "typename ...T" then, and that it only works in C++0x. But the above compiled in strict C++03 mode. What's going on?

Answer 1

It's just the bad old C varargs syntax; the grammar allows omitting the comma. The following are equivalent:

int printf(const char* fmt, ...);
int printf(const char* fmt...);

Answer 2

Did you call the function? Template functions don't get compiled until you call them. And in Visual Studio 2010, IntelliSense shows the real syntax of that function would be

template <class T> void f(T&, ...)

Smells like old variable argument syntax.