GCC check the reference type is same with value

Question

It's amazing that std::set be converted to MySet, but how to avoid ?

#include <bits/stdc++.h>

struct MySet : public std::set<int> {
  MySet(const std::set<int>& s) {
  }
};

std::set<int> get(int i) {
  return std::set<int>{i};
}

int main() {
  const MySet& a = get(0);
  std::cout << a.empty() << std::endl;  // true
}

const MySet& a = get(0); should give compile error.

Answer 1

const MySet& a = get(0); should compile error

This can be done either by removing the converting ctor MySet::MySet(const std::set<int>&)or by making it explicit as shown below:

struct MySet : public std::set<int> {
//vvvvvvvv---------------------------------->make this ctor explicit
  explicit MySet(const std::set<int>& s) {
  }
};

int main() {
  const MySet& a = get(0);
  std::cout << a.empty() << std::endl;  // gives error now
}