c++ - member template in class template

class member template can be useful in many situation.

 

The good side of member template is that there could be infinite set of number of nested classes CL and potential infinite number of member function assign().

 

 

/**
* file
*  member_templates.h
* description:
*   this is a file that demonstrate the use of the member template inside template classes
*/

#include <iostream>
#include <string>

using std::string;
using std::ostream;
using std::istream;
using std::cerr;
using std::cout;
using std::endl;
using std::exit;


template<class Type>
class QueueItem
{
public:
	QueueItem(const Type &val) : next(0), value (val)  {} 
	//~QueueItem() ;
//	Type value() { return this->value; }
//	QueueItem<Type> next() { return this->next; }
//private:
	QueueItem<Type> *next;
	Type value;
protected:
};


template <class Type>
class Queue 
{
public:
	Queue() : front(0), back (0) {} 
	~Queue() ;
	Type remove();
	void add(const Type &);
	bool is_empty() const {
		return front == 0;
	}

	// class member template
	// with this you can define 
	// things like Queue<int>::CL<string> ...
	// which may sound useless at the frist glance, but we will see
	template <class T>
	class CL
	{
		T name;
		Type mem;
	};

	template <class Iter>
	void assign(Iter first, Iter last)
	{
		while (!is_empty()) 
			remove(); // call Queue<T>::remove
		for (; first != last; ++first) 
			add(*first);
	}

private:
	QueueItem<Type> *front;
	QueueItem<Type> *back;
protected:
};


// if it does not have a good destructor, then do not provide one.
//template <class Type>
//QueueItem<Type>::~QueueItem()
//{
//	
//}


template <class Type>
Queue<Type>::~Queue()
{
	while (!is_empty()) {
		remove();
	}
}

template <class Type>
void Queue<Type>::add(const Type &val)
{

	QueueItem<Type> *pt = new QueueItem<Type>(val);
	if (is_empty())
	{
		front = back = pt;
	}
	else 
	{
		back->next = pt;
	}
	
}


template <class Type>
Type Queue<Type>::remove()
{
	if (is_empty()) {
		cerr << "remove() on empty queue\n";
		exit(-1);
	}
	QueueItem<Type> *pt = front;
	front = front->next;
	Type retval =  pt->value;
	delete pt;
	return retval;
}

 

and belowis the implementeation code as below.

 

/**
* file
*  member_templates.cppp
* description:
*   this is a file that demonstrate the use of the member template inside template classes
*/

#include "member_templates.h"
#include <vector>
#include <iostream>
#include <string>
#include <list>

using std::vector;
using std::cout;
using std::string;
using std::list;

void demo_class_templates()
{
	Queue<int> qi;

	vector<int> vsi;

	qi.assign(vsi.begin(), vsi.end());

	list<int> lp;

	qi.assign(lp.begin(), lp.end());

	list<int*> lvp;

	//qi.assign(lvp.begin(), lvp.end());
}