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Now that was a very nice and clean solution which solved all problems, which I actually didn't think of.
So, appending & after the type to specify a reference would expand it just like in the normal...

What "version" of the program? Both with and without decltype in foo3/4 works with Clang, but decltype for foo3/4 does not work with Visual Studio, which is the problem.

You need the experimental compiler for 2012:
Download Visual C++ Compiler November 2012 CTP from Official Microsoft Download Center

2010 and 2012 (out of the box) doesn't support variadic...

Consider this code:

#include <iostream>
#include <string>
#include <algorithm>
#include <iterator>
#include <cctype>
#include <fstream>
#include <vector>
#include <type_traits>