Third round of feature requests in To Do List exercise (week 2)

ToDoList_3.h

#include <iostream>
#include <string>
#include <vector>
#include <ctime>

static int taskNumberCounter = 0;				// Static variable to assign a taskNumber to task

enum Status {done, notDone};

enum Priority {none, low, medium, high};

enum Visibility {Visible, NotVisible};				// Public means that friends can view the task				

class User {
private:
	std::string name;
	std::vector<User> listOfFriends;
	List l;

public:
	
	std::vector<User> getListOfFriends();
	// We can have some UI element call returnNumOfPublicTasks when this method is called, so that when a user views a friend's list, 
	//		the number of tasks in that friend's list will be available.
	List viewFriendsListOfTasks(User &u);				// This will call the input user's list via viewTaskListByVisibility()

   	// This will call viewTaskListByVisiblity(public) for all users and return the number of tasks with the same name
  	int getNumUsersWithSameTaskName(std::string taskName);
};

class Task {
private:
	
	int taskNumber;
	std::string name;
	Status currStatus = notDone;
  	Priority currPriority = none;
	time_t dueDate;	
	Visibility currVisibility = NotVisible;
	
public:

	Task(std::string name, Status s);			// Assigns a taskNumber and increments taskNumberCounter
	
	void setName(std::string newName);
	void setStatus(Status newStatus);
	void setPriority(Priority newPriority);
	void setDueDate(timt_t newDueDate);
	void setVisibility(Visibility newVisibility);
};

class List {
private:	

	std::vector<Task> taskList;

public:
	
	List(Task &t);						// Creates a List, note that instantiation of a List requires a Task

	// Accessors
	Task getTask(int taskNumber);
	
	// Mutators for taskList 
	void addTaskToList(Task &t);				// Creates a task object and adds it to taskList
	void deleteTaskFromList(Task &t);			// If this causes taskList.empty(), delete List

	int getNumOfTasks();					// Returns number of tasks in taskList
	int getNumOfVisibleTasks();				// Returns number of tasks in taskList 
	
	std::vector<Task> viewTaskList();			// Returns a copy of taskList
	std::vector<Task> viewTaskListDateSort(bool asc);	// Returns list of tasks sorted by Date, ascending or descending
	std::vector<Task> viewTaskListByStatus(Status s);	// Returns list of tasks filtered by status
	std::vector<Task> viewTaskListByPriority(Priority p);	// Returns list of tasks filtered by priority
	std::vector<Task> viewTaskListByVisiblity(Visiblity v);	// Returns list of tasks filtered by visilbity, empty list if none visible
};

I definitely feel that I've fallen into a bit of a trap here. The idea of having to search every User's List(s) to find matching Task name does not seem like a bug to me, but it does seem at least very slow. Further, since this feature request asks to display the total number of items in the List currently being viewed, I don't feel that my current design strongly captures the notion of whether or not a List is currently being viewed.