Подскажите по проблемем с макросами, пожалуйста

struct Date {
    int year, month, day;
};
 
struct Time {
    int hours, minutes;
};
 
struct AirlineTicket {
    string from;
    string to;
    string airline;
    Date departure_date;
    Time departure_time;
    Date arrival_date;
    Time arrival_time;
    int price;
};

vector<AirlineTicket> tixs = {
        { "VKO", "AER", "Utair", { 2018, 2, 28 }, { 17, 40 }, { 2018, 2, 28 }, { 20, 0 }, 1200 },
        { "AER", "VKO", "Utair", { 2018, 3, 5 }, { 14, 15 }, { 2018, 3, 5 }, { 16, 30 }, 1700 },
        { "AER", "SVO", "Aeroflot", { 2018, 3, 5 }, { 18, 30 }, { 2018, 3, 5 }, { 20, 30 }, 2300 },
        { "PMI", "DME", "Iberia", { 2018, 2, 8 }, { 23, 00 }, { 2018, 2, 9 }, { 3, 30 }, 9000 },
        { "CDG", "SVO", "AirFrance", { 2018, 3, 1 }, { 13, 00 }, { 2018, 3, 1 }, { 17, 30 }, 8000 },
};

#define SORT_BY(field)

sort(begin(tixs), end(tixs), SORT_BY(price));

#define SORT_BY(field) [](const AirlineTicket &v1,  const AirlineTicket &v2) {return v1.field < v2.field;}