Add void specialization for self_relative_ptr

Author: igchor

include/libpmemobj++/experimental/self_relative_ptr.hpp

@@ -21,6 +21,43 @@ namespace obj
 namespace experimental
 {
 
+template <typename T>
+class self_relative_ptr;
+
+template <>
+class self_relative_ptr<void> : public self_relative_ptr_base {
+public:
+	using base_type = self_relative_ptr_base;
+	using this_type = self_relative_ptr;
+	using element_type = void;
+
+	constexpr self_relative_ptr() noexcept = default;
+
+	constexpr self_relative_ptr(std::nullptr_t) noexcept
+	    : self_relative_ptr_base()
+	{
+	}
+
+	self_relative_ptr(element_type *ptr) noexcept
+	    : self_relative_ptr_base(self_offset(ptr))
+	{
+	}
+
+	inline element_type *
+	get() const noexcept
+	{
+		return static_cast<element_type *>(
+			self_relative_ptr_base::to_void_pointer());
+	}
+
+private:
+	difference_type
+	self_offset(element_type *ptr) const noexcept
+	{
+		return base_type::pointer_to_offset(static_cast<void *>(ptr));
+	}
+};
+
 /**
  * Persistent self-relative pointer class.
  *