Implementation of a slotmap

slotmap.cpp

#include <iostream>
#include <algorithm>
#include <string>
#include <memory>
#include <vector>

using namespace std;
using u32 = unsigned int;
using s32 = int;

struct Texture
{
	s32 m_id;
	string m_debugname;
	
	Texture(s32 id, const std::string& debugname)
	{ 
		m_debugname = debugname; m_id = id;
		// + allocate texture data
		 std::cout << "Creating texture (" << m_debugname << ")" << std::endl; 
	}
	~Texture() 
	{ 
	    if(m_id == -1)
		    {
		        // + free texture data
		        std::cout << "Destructing texture (" << m_debugname << ")" << std::endl; 
		    }
	}

	// "Holy Trinity"
	Texture(const Texture& other) :
		m_id{ other.m_id },
		m_debugname{ other.m_debugname }
	{
	}
	
	void swap(Texture &other)
	{
		using std::swap;
		swap(m_id, other.m_id);
		swap(m_debugname, other.m_debugname);
	}
	
	Texture& operator=(const Texture& other)
	{
		Texture{ other }.swap(*this);
		return *this;
	}

};

template<class T>
class Slotmap
{
public:
	std::vector<T>	    m_resources;
	std::vector<u32>	m_freelist;

	Slotmap()
	{
	}

	~Slotmap()
	{
		std::cout << "\n(Destruction of the slot map)\n";
		destroyAll();
		
	}

	void printAll()
	{
		std::cout << "List of objects : ";
		for (auto& elt : m_resources) 
		{
			std::cout << "[" << elt.m_debugname << " / " << elt.m_id<< "]\t";
		}
		std::cout << "\n";
	}

	template <class ... Args>
	u32 add(Args&& ... args)
	{
		if (!m_freelist.empty())
		{
			u32 free = m_freelist.back();
			m_freelist.pop_back();
			m_resources[free] = T(free, args...);
			return free;
		}
		else
		{
			u32 id = m_resources.size();
			m_resources.emplace_back(id, args...);
			return id;
		}
	}

	void destroy(u32 id)
	{
		m_resources[id].m_id = -1;
		m_freelist.emplace_back(id);
		std::cout << m_resources[id].m_debugname << " is marked for deletion\n";
	}
	
	void destroyAll()
	{
		std::for_each(std::begin(m_resources), std::end(m_resources), [](T& t) {t.m_id = -1; });
	}
};


int main() {
	Slotmap<Texture> textureManager{};
	//textureManager.m_resources.reserve(16);
	u32 o1 = textureManager.add("OBJ1");
	textureManager.printAll();
	u32 o2 = textureManager.add("OBJ2");
	textureManager.printAll();
	u32 o3 = textureManager.add("OBJ3");
	textureManager.printAll();
	textureManager.destroy(o2);
	textureManager.printAll();
	u32 o4 = textureManager.add("OBJ4");
	textureManager.printAll();
	return 0;
}

// The above code generates this trace
/*
Creating texture (OBJ1)
List of objects : [OBJ1 / 0]	
Creating texture (OBJ2)
List of objects : [OBJ1 / 0]	[OBJ2 / 1]	
Creating texture (OBJ3)
List of objects : [OBJ1 / 0]	[OBJ2 / 1]	[OBJ3 / 2]	
OBJ2 is marked for deletion
List of objects : [OBJ1 / 0]	[OBJ2 / -1]	[OBJ3 / 2]	
Creating texture (OBJ4)
Destructing texture (OBJ2)
List of objects : [OBJ1 / 0]	[OBJ4 / 1]	[OBJ3 / 2]	
(Destruction of the slot map)
Destructing texture (OBJ1)
Destructing texture (OBJ4)
Destructing texture (OBJ3)
*/