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MSVC's extern template feature is mostly the same as what is
standardized. However, it was implemented before it was considered for
standardization and VC11 is the first version that implements the
The big difference is that you don't need the ifdef around the extern
in header, because the standard allows you to have:
extern template Holder<int>;
Versions of MSVC before 11 require that you not have the extern before
the explicit instantiation.