im not sure why i wrote this

gistfile1.cpp

#include <cstdlib>
#include <iostream>
#include <queue>
#include <stdexcept>

struct policy
{
};

struct allocator: policy
{
	virtual void * allocate(std::size_t size) = 0;
};

struct heap_allocator: allocator
{
	virtual void * allocate(std::size_t size)
	{
		std::cout << "stack allocating " << size << " bytes" << std::endl;
		return std::malloc(size);
	}
};

struct debug_allocator: allocator
{
	virtual void * allocate(std::size_t size)
	{
		std::cout << "debug allocating " << size << " bytes" << std::endl;
		return std::malloc(size);
	}
};

static std::deque<allocator *> allocator_stack;

template <typename T>
struct use
{
	use()
	{
		allocator_stack.push_back(new T());
	}
	~use()
	{
		T * back = static_cast<T *>(allocator_stack.back());
		delete back;
		allocator_stack.pop_back();
	}
};

void * allocate(std::size_t size)
{
	if (allocator_stack.empty())
	{
		throw std::runtime_error("There is no allocator on the stack!");
	}
	allocator * back = allocator_stack.back();
	return back->allocate(size);
}

void hello_world()
{
	use<heap_allocator> scope1;
	char * data1 = static_cast<char *>(allocate(1024));
	use<debug_allocator> scope2;
	char * data2 = static_cast<char *>(allocate(1024));
}

int
main()
{
	hello_world();
}