// namespace-main-13-14.cpp		By: Aiman Hanna -  ©1993-2006 Aiman Hanna

// This program illustrates the name "using directives".
// Namespaces were introduced with standard C++. Prior C++ implementations
// did not support namespaces. As a consequence, pre-standard libraries did not wrap 
// their global declarations in namespaces. Since an important amount of C++ code 
// were written before namespaces were defined, it was not possible to just enclose 
// the content of these libraries in namespaces; this would simply break all old 
// applications. 
// The "using declaration" can be used to solve this problem, however if the library 
// is quite large and the old applications uses many of the library names, then a 
// large number of using declarations has to be added, which is both tedious and 
// error-prone. To solve this problem, the "using directive" can be used. The 
// utilization of using directive eases the migration between the old and the new 
// library versions. 
// The using directive begins with "using namespace" followed by the namespace name. 
// A using directive allows us to make all the names from a specific namespace visible 
// in their short form. 
// A using directive makes the namespace members visible as if they were declared 
// outside the namespace at the location where the namespace definition is located. 
// For example: 
// 		namespace A{
//					int i, j;
// 		           }
// looks like: 
// 		int i, j;
// to all codes that have the following using directive in their scope:
//		using namespace A;

// Although using directives are simple to use; with a single using directive, are 
// the namespace member names are suddenly visible. Although this may seem like a 
// simple solution to, it may introduce its won problems. If an application uses its 
// uses many libraries, and if the names within these libraries are made visible with 
// using directives, then we are back to point zero; the global space pollution problem
// reappears. 

// Key points:  1) Using Directives


#include "namespace14.h"

int main()
{
	
// The following using declarations are introduced inside the main() function; as a 
// result they are only in effect inside this function. 


using namespace region3;
using namespace region31;
using namespace region32;
using namespace region33;

using namespace region4;



	Greeting();

	Calc1 c1(30), c11(45);;
	c1.setValue(32);

	Calc2 c2;
	c2.setValue(c1);
	cout << "The value of object \"c2\" has been set to : " << c2.getValue() << endl; 

	// use the global object - set it to the same value as c1

	region4::dup.setValue(c1);  // must have its fully qualified name; otherwise ambiguous
	cout << "The value of object \"dup\" has been set to : " << region4::dup.getValue() << endl; 

	region3::dup(c1, c11);      // must have its fully qualified name; otherwise ambiguous
	cout << "The value of object \"c1\" has been set to : " << c1.getValue() << endl; 

	cout << "\n\n==============================================\n";
	message1();
	message2();
	message3();
	cout << "==============================================\n";
	return 0;
}

// The result of running the program
/*
Hello from region 3.
The value of object "c2" has been set to : 32
The value of object "dup" has been set to : 32
The value of object "c1" has been set to : 45


==============================================
Hello...there...That is a bit better! Right?
==============================================

*/