Googling for your error message, this looks related to a compiler bug that was reduced to a known Defect Report concerning the trailing return type:
1433. trailing-return-type and point of declaration
Section: 3.3.2 [basic.scope.pdecl] Status: extension
Submitter: Jason Merrill Date: 2011-12-20 This seems like it should be well-formed:template <class T> T list(T x); template <class H, class ...T> auto list(H h, T ...args) -> decltype(list(args...)); auto list3 = list(1, 2, 3);
but it isn't, because the second list isn't in scope in its own trailing-return-type; the point of declaration is after the declarator, which includes the trailing-return-type. And since int has no associated namespaces, the call in the return type only sees the first list. G++, EDG and Clang all reject the testcase on this basis.
But this seems like a natural pattern for writing variadic function templates, and we could support it by moving the point of declaration to the ->. This would mean having to deal with a function that only has a placeholder for a return type, but I think we can handle that.
Rationale (February, 2012):
This is a request for an extension to the language and is thus more appropriately addressed by EWG.