#include <iostream>
#include <map>

class W {
    public:
        W() { std::cout << "W()\n"; }
        W(int a) : a_(a) { std::cout << "W(int a)\n"; }
        int get_a() { return a_; }
    private:
        int a_;
};

void foo(W bar) {
    std::map<int, W> map;
    map[bar.get_a()] = bar;
}

int main() {
    foo(W(10));
    return 0;
}