C++ inset is not a replacement for Rust Element API

test.cpp

#include <iostream>
#include <functional>
#include <unordered_map>

class HiMike {
private:
    int value;
public:
    HiMike(int value) : value(value) { }
    friend class std::hash<HiMike>;
    friend bool operator==(const HiMike&, const HiMike&);
};

bool operator==(const HiMike& a, const HiMike& b) {
   return a.value == b.value;
}

namespace std {
   template<>
   class hash<HiMike> {
   public:
      typedef HiMike argument_type;
      typedef size_t result_type;

      result_type operator()(const argument_type& hi) const {
         cerr << "Hash for " << hi.value << endl;
         return hash<int>{}(hi.value);
      }
   };
}


int main() {
  std::unordered_map<HiMike, int> hihash;
  hihash[HiMike(0)] = 42;

  HiMike odin{1};

  auto it = hihash.find(odin);
  std::cerr << "sizeof=" << sizeof(it) << ", it is end: " << (it == hihash.end()) << std::endl;
  hihash.insert(it, {odin, 2});

  std::cerr << hihash[odin] << std::endl;
  return 0;
}

/*

ib@monoid:/tmp$ clang++-6.0 -std=c++17 -O3 test.cpp  
ib@monoid:/tmp$ ./a.out 
Hash for 0
Hash for 1
sizeof=8, it is end: 1
Hash for 1
Hash for 1
2
ib@monoid:/tmp$ g++ --std=c++17 -O3 test.cpp 
ib@monoid:/tmp$ ./a.out 
Hash for 0
Hash for 1
sizeof=8, it is end: 1
Hash for 1
Hash for 1
2

*/