C++ Sorting set using custom comparator in a container class

Question

I have a class Person that has a name and an age.

I have a container class called people that stores a set of persons.

I have created two custom comparators to sort by name and by age.

When I store the set containing Persons in my class (People) how do pass the custom comparator in.

for Example

My comparator looks like this

struct compareByName
{
    bool operator()(const Person & Left, const Person & Right)
    {
        return (Left.getName() < Right.getName());
    }
};

in the main if I want to sort a set of persons by name I just do

set<Person, compareByName> peopleByName;

or for age I do

set<Person, compareByAge> peopleByAge;

Where I am having trouble is How do I use this in my people container class I would have something like

class People
{
private:
    set<Person, COMPARATOR> m_people;
}

where COMPARATOR could either be by name or age

Answer 1

You can use std::function as comparator type and then provide particular comparator for constructor:

class People
{
    using PeopleSet = set<Person, std::function<bool(const Person &p1, const Person &p2 )>>;

    People() : people( compareByName() ) {}
    void sortByAge();
private:
    PeopleSet people; 
};

note you cannot change comparator after creation of set, you have to create another instance:

void People::sortByAge()
{
    people = PeopleSet( people.begin(), people.end(), compareByAge() );
}

and that would involve copying or moving whole set. If you want to be able to use both ways at the same time use boost::multi_index instead.