18.16.txt

			-- using declarations --
a)
namespace Exercise {
	int ivar = 0;
	double dvar = 0;
	const int limit = 1000;
}

int ivar = 0;
using Exercise::ivar;
using Exercise::dvar;
using Exercise::limit;
void manip() {
	double dvar = 3.1416;
	int iobj = limit + 1;
	++ivar;
	++::ivar;
}
// using declaration of Exercise::ivar is an error, can't declare an alias
// with the same name as ivar, as it is in the current scope
// dvar and limit is added to the global scope as a local alias from the Exercise namespace
// manip declares a variable named dvar, that hides the outer scope's dvar
// iobj is initialized to Exercise::limit + 1
// if we removed the erroneous using declaration, both incrementing of ivar would increment
// the global one

b)
namespace Exercise {
	int ivar = 0;
	double dvar = 0;
	const int limit = 1000;
}

int ivar = 0;
void manip() {
	using Exercise::ivar;
	using Exercise::dvar;
	using Exercise::limit;
	double dvar = 3.1416;
	int iobj = limit + 1;
	++ivar;
	++::ivar;
}
// ivar, dvar and limit from the namespace Exercise is put into manip as a local alias
// the declaration of ivar hides the global ivar inside the manip function
// the declaration of dvar after the using declaration of Exercise::dvar would be an error
// ++ivar increments Exercise::ivar
// ++::ivar increments ivar in the global scope

			-- using directive --
a)
namespace Exercise {
	int ivar = 0;
	double dvar = 0;
	const int limit = 1000;
}

int ivar = 0;
using namespace Exercise;
void manip() {
	double dvar = 3.1416;
	int iobj = limit + 1;
	++ivar;
	++::ivar;
}
// using directive lifts Exercise's members in the nearest scope that contains Exercise and the directive:
// into the global scope
// clash between ::ivar and Exercise::ivar, detected only if ivar is used
// declaration of dvar inside manip hides the dvar inside the global scope
// ++ivar is ambiguous: global ivar, or Exercise::ivar?
// ++::ivar increments the global ivar (::ivar is a qualified name)

b)
namespace Exercise {
	int ivar = 0;
	double dvar = 0;
	const int limit = 1000;
}

int ivar = 0;
void manip() {
	using namespace Exercise;
	double dvar = 3.1416;
	int iobj = limit + 1;
	++ivar;
	++::ivar;
}
// using directive lifts Exercise's members in the nearest scope that contains Exercise and the directive:
// into the global scope
// clash between ::ivar and Exercise::ivar, detected only if ivar is used
// declaration of dvar inside manip hides the dvar inside the global scope
// ++ivar is ambiguous: global ivar or Exercise::ivar?
// ++::ivar increments the global ivar (::ivar is a qualified name)