模板笔记5 模板的模板参数

#include <iostream>
#include <deque>
#include <stdexcept>
#include <memory>
#include <vector>
template<typename T, template<typename ELEM, typename = std::allocator<ELEM>> class CONT = std::deque>
class Stack{
private:
CONT<T> elems;
public:
void push(T const&);
void pop();
T top() const;
bool empty() const{
return elems.empty();
}
template<typename T2, template<typename ELEM2, typename = std::allocator<ELEM2>> class CONT2>
Stack<T, CONT>& operator=(Stack<T2, CONT2> const&);
};

template<typename T, template<typename,typename> class CONT>
void Stack<T,CONT>::push (T const& elem)
{
elems.push_back(elem);
}

template<typename T, template<typename,typename> class CONT>
void Stack<T, CONT>::pop ()
{
if(elems.empty())
{
throw std::out_of_range("Stack<>::pop():empty stack");
}
elems.pop_back();
}

template<typename T, template<typename, typename> class CONT>
T Stack<T,CONT>::top () const
{
if(elems.empty()){
throw std::out_of_range("Stack<>::top():empty top stack");
}
return elems.back();
}

template<typename T, template<typename,typename> class CONT>
template<typename T2, template<typename, typename> class CONT2>
Stack<T,CONT>& Stack<T,CONT>::operator=(Stack<T2,CONT2> const& op2)
{
if ((void *)this == (void *)&op2) {
return *this;
}
Stack<T2,CONT2> tmp(op2);
elems.clear();
while (!tmp.empty()) {
elems.push_front(tmp.top());
tmp.pop();
}
return *this;
}

int main()
{
try{
Stack<int> intStack;
Stack<float> floatStack;

intStack.push(42);
intStack.push(7);

floatStack.push(7.7);

floatStack = intStack;

std::cout << floatStack.top() << std::endl;
floatStack.pop();
std::cout << floatStack.top() << std::endl;
floatStack.pop();
std::cout << floatStack.top() << std::endl;
floatStack.pop();
}
catch (std::exception const& ex)
{
std::cerr << "Exception: " << ex.what() << std::endl;
}
Stack<int, std::vector> vStack;

vStack.push(42);
vStack.push(7);
std::cout << vStack.top() << std::endl;
vStack.pop();
}