accidentalcopy.cc

// % g++ --std=c++14 accidentalcopy.cc -o accidentalcopy
// % ./accidentalcopy
// This prints the output:
//
// 42 = 42
// 42 = 42
// accidentalcopy(13656,0x117fc45c0) malloc: *** error for object 0x7fd967402b20: pointer being freed was not allocated
// accidentalcopy(13656,0x117fc45c0) malloc: *** set a breakpoint in malloc_error_break to debug

#include <iostream>

class Repo {

public:

  Repo()
    : fortyTwo_{new int{42}} {}

  ~Repo() {
    std::cout << "42 = " << *fortyTwo_ << std::endl;
    delete fortyTwo_;
  }

  // I define this a little later
  static Repo& get();

  int* fortyTwo_ = nullptr;
};

// This is the only Repo that's supposed to exist
Repo s_repo;

Repo& Repo::get() {
  return s_repo;
}

int main() {
  // Should be `Repo& repo1 = Repo::get()`
  // Leaving the `&` off makes an extra copy, which means we delete fortyTwo_ twice...
  Repo repo1 = Repo::get();
  return 0;
}