16.25.txt

Exercise 16.25: Explain the meaning of these declarations:

	extern template class vector<string>;
	template class vector<Sales_data>;

By Faisal Saadatmand

	extern template class vector<string>;

This is an 'explicit instantiation' of the form 'declaration'. (P. 675) The
extern template declaration informs the compiler that this template has been
instantiated somewhere else in the program (in a different compiled source
file). As a result, the compiler will not generate code to instantiated this
class template in the current file.

	template class vector<Sales_data>;

This is also an 'explicit instantiation'; however, it is of the form
'definition'. (Ibid.) In this case the compiler will generate code for the
class instantiation in the current file, because there is no 'extern' promise
that it was instantiated somewhere else.