std::unordered_set::operator=

// unordered_set::operator=
#include <iostream>
#include <string>
#include <unordered_set>

template<class T>
T cmerge (T a, T b) {
  T t(a); t.insert(b.begin(),b.end()); return t;
}

int main ()
{
  std::unordered_set<std::string> first, second, third;
  first = {"red","green","blue"};      // init list
  second = {"orange","pink","yellow"}; // init list
  third = cmerge (first, second);      // move
  first = third;                       // copy

  std::cout << "first contains:";
  for (const std::string& x: first) std::cout << " " << x;
  std::cout << std::endl;

  return 0;
}