Does std::greater work when you have a std::pair of int and a class?
I am trying to create a priority queue of pairs, ordered by the first element:
std::priority_queue<std::pair<double, classA>, std::vector<std::pair<double, classA>>, std::greater<std::pair<double, classA>>> priorityQueue
But I get an error that says
no match for 'operator<'`
And it alludes to the second element of the std::pair, which is of class type.
Is std::greater applied to the first and second elements of the std::pair?
std::greater is just a wrapper for a call to operator < of the template type. For std::pair we can check the reference site here and we see it says
Compares lhs and rhs lexicographically by
operator<, that is, compares the first elements and only if they are equivalent, compares the second elements.
So, it uses the operator < of both types, which means your class type needs to supply it. Since it doesn't you get the compiler error.