18.16.txt

Exercise 18.16: Explain the following code assuming using declarations for all
the members of namespace Exercise are located at the location labeled position
1. What if they appear at position 2 instead? Now answer the same question but
replace the using declarations with a using directive for namespace Exercise.

	namespace Exercise {
		int ivar = 0;
		double dvar = 0;
		const int limit = 1000;
	}
	int ivar = 0;
	// position 1
	void manip() {
		// position 2
		double dvar = 3.1416;
		int iobj = limit + 1;
		++ivar;
		++::ivar;
	}

By Faisal Saadatmand

Moving all the using declarations from position 1 to position 2 has the effect
of making the Exercise namespace members visible to the local (rather than the
global) scope of mainip function. The effect is that Exercise::ivar will hide
::ivar and Exercise::dvar will conflict with mainp::dvar, which will give us a
compile error.

If we replace the using declarations with a using directive instead, it would
inject names from Exercise into the global scope. The effect is that ::ivar
would conflict with Exercise::ivar, but we would not get a compile error until
ivar is used: ++ivar is in error because it is ambiguous but ++::ivar is fine.
Moreover, main::dvar would hide Exercise:dvar.