#include <map>

struct a {
    std::map<int, int> x;
    
    a() : x({{1,2}, {3,4}}) {}
};

struct b {
    std::map<int, int> x;
    
    b() : x{{1,2}, {3,4}} {}
};

int main() {
    a a1;
    b b1;
}