gplib/include/gp/variant.hpp

#pragma once
#include <gp/algorithm/tmp_manip.hpp>
#include <type_traits>
#include <new>
#include "gp_config.hpp"
#include "gp/exception.hpp"
#include "gp/memory.hpp"
#include "gp/function.hpp"


namespace gp{

	template<typename ...T>
	class fixed_variant{
		std::size_t index = std::numeric_limits<std::size_t>::max();
		char buffer[max_size<T...>()];
		gp::function<void(void*)> dtor = [](void*){};
		static_assert(all_of_fixed_size<T...>::value, "not fixed");
	public:
		template<typename U, typename std::enable_if<list_contains_class<U,T...>::value,int>::type>
		constexpr fixed_variant(U& value)
		: index{r_index_of<U, T...>::value}
		{
			new(buffer) U(value);
			dtor = gp::function([](void* thing){((U*)thing)->~U();});
		}

		template<typename U, typename std::enable_if<list_contains_class<U,T...>::value,int>::type>
		constexpr fixed_variant(U&& value)
		: index{r_index_of<U, T...>::value}
		{
			new(buffer) U(std::move(value));
			dtor = gp::function([](void* thing){((U*)thing)->~U();});
		}



		template<typename U, typename std::enable_if<list_contains_class<U,T...>::value,int>::type>
		void operator=(U& value)
		{
			if(index != std::numeric_limits<std::size_t>::max())
			{
				dtor((void*)buffer);
			}
			index = r_index_of<U, T...>::value;
			new(buffer) U(value);
			dtor = gp::function([](void* thing){((U*)thing)->~U();});
		}

		template<typename U, typename std::enable_if<list_contains_class<U,T...>::value,int>::type>
		void operator=(U&& value)
		{
			if(index != std::numeric_limits<std::size_t>::max())
			{
				dtor((void*)buffer);
			}
			index = r_index_of<U, T...>::value;
			new(buffer) U(std::move(value));
			dtor = gp::function([](void* thing){((U*)thing)->~U();});
		}

		~fixed_variant()
		{
			if(index != std::numeric_limits<std::size_t>::max())
			{
				dtor((void*)buffer);
			}
		}

		template<typename U>
		constexpr U& value()
		{
			if constexpr (gp_config::has_exceptions)
			{
				if(r_index_of<U, T...>::value != index)
				{
					throw bad_variant_access<U>{};
				}
			}
			return *reinterpret_cast<U*>(buffer);
		}

		template<typename U>
		constexpr U& is_a()
		{
			if(r_index_of<U, T...>::value == index)
			{
				return true;
			}
			else
			{
				return false;
			}
		}
	};

	template<typename allocator_t = gp_config::memory_module::default_allocator, typename ...T>
	class variant{
		std::size_t index = std::numeric_limits<std::size_t>::max();
		void* ptr;
		gp::function<void(void*)> dtor = [](void*){};
		allocator_t allocator;
	public:
		template<typename U, typename std::enable_if<list_contains_class<U,T...>::value,int>::type>
		constexpr variant(U& value)
		: index{r_index_of<U, T...>::value}
		{
			ptr = (void*)new(allocator.allocate(sizeof(U))) U(value);
			dtor = gp::function([](void* thing){((U*)thing)->~U();}); // TODO:replae with delete(p,t)
		}

		template<typename U, typename std::enable_if<list_contains_class<U,T...>::value,int>::type>
		constexpr variant(U&& value)
		: index{r_index_of<U, T...>::value}
		{
			ptr = (void*)new(allocator.allocate(sizeof(U))) U(std::move(value));
			dtor = gp::function([](void* thing){((U*)thing)->~U();}); // TODO:replae with delete(p,t)
		}

		template<typename U, typename std::enable_if<list_contains_class<U,T...>::value,int>::type>
		void operator=(U& value)
		{
			if(index != std::numeric_limits<std::size_t>::max())
			{
				dtor(ptr);
				allocator.deallocate(ptr);
			}
			index = r_index_of<U, T...>::value;
			ptr = (void*)new(allocator.allocate(sizeof(U))) U(value);
			dtor = gp::function([](void* thing){((U*)thing)->~U();}); // TODO:replae with delete(p,t)
		}

		template<typename U, typename std::enable_if<list_contains_class<U,T...>::value,int>::type>
		void operator=(U&& value)
		{
			if(index != std::numeric_limits<std::size_t>::max())
			{
				dtor(ptr);
				allocator.deallocate(ptr);
			}
			index = r_index_of<U, T...>::value;
			ptr = (void*)new(allocator.allocate(sizeof(U))) U(std::move(value));
			dtor = gp::function([](void* thing){((U*)thing)->~U();}); // TODO: replace with delete(p, t)
		}

		~variant()
		{
			if(index != std::numeric_limits<std::size_t>::max())
			{
				dtor(ptr);
				allocator.deallocate(ptr);
			}
		}

		template<typename U>
		constexpr U& value()
		{
			if constexpr (gp_config::has_exceptions)
			{
				if(r_index_of<U, T...>::value != index)
				{
					throw bad_variant_access<U>{};
				}
			}
			return *reinterpret_cast<U*>(ptr);
		}

		template<typename U>
		constexpr U& is_a()
		{
			if(r_index_of<U, T...>::value == index)
			{
				return true;
			}
			else
			{
				return false;
			}
		}
	};
}