Could be somewhat useful.
#include <iostream>#include <algorithm>#include <vector>using namespace std;struct Foo { std::vector<int> v = {1,2,3};};bool operator==(const Foo& foo, int i) { return std::any_of(foo.v.begin(), foo.v.end(), [=](int v){ return v == i; });}int main() { Foo a; if (a==1 && a==2 && a==3) cout << "Really??"<< endl; return 0;}