18.20.txt

namespace primerLib {
	void compute();
	void compute(const void *);
}
using primerLib::compute;			// puts void compute(), and void compute(const void *) in the global scope
void compute(int);
void compute(double, double = 3.4);
void compute(char*, char* = 0);

// candidate functions:
// void compute() from primerLib
// void compute(const void *) from primerLib
// void compute(int)
// void compute(double, double = 3.4);
// void compute(char*, char* = 0);

void f()
{
	compute(0);
	// void compute() not viable
	// void compute(const void *) viable: 0 can be converted to a pointer
	// void compute(int) viable: exact match -> this is called
	// void compute(double, double = 3.4) viable: through int to double conversion
	// void compute(char*, char* = 0) viable: through pointer conversion
}

if the using declaration were located in main before the call to compute:
f would see only the global functions as candidates:
	void compute(int),						exact match
	void compute(double, double = 3.4)		double conversion
	void compute(char*, char* = 0);			pointer conversion
void compute(int) is called because it is an exact match