Ytdyklly

I thought a singleton set manager is better than a global set. So I wrote a singleton set manager class C.

Minimal requirement of the class C

1. must have insert() to insert a new item(int)


2. must have has() to check if it has the item


3. should be a singleton

Questions

1. I wonder this is a good singleton implementation or not.


2. How can I make this code better?

Code

#include <iostream>

#include <iterator>

#include <set>

#include <vector>

#include <initializer_list>



class C {

  std::set<int> s;



public:

  static C &getInstance() {

    static C instance;

    return instance;

  }



  bool insert(int i) {

    std::pair<std::set<int>::iterator, bool> ret = s.insert(i);

    return ret.second;

  }



  bool has(int i) {

    return s.find(i) != s.end();

  }



  /* dump() is not essential */

  void dump() {

    std::copy(s.begin(), s.end(),

              std::ostream_iterator<int>(std::cout, " "));

    std::cout << "n";

  }



private:

  C() {}

  /* prevent to call C(C const &) */

  C(C const &);

  /* prevent to call operator=() */

  void operator=(C const &);

};



void foo(std::vector<int> &v) {

  C &c = C::getInstance();

  for (int i = 0; i < v.size(); i++) {

    c.insert(v[i]);

  }

}



void bar(std::vector<int> &v) {

  C &c = C::getInstance();

  for (int i = 0; i < v.size(); i++) {

    std::cout << v[i] << " " << (c.has(v[i]) ? "y " : "n ");

  }

  std::cout << "n";

}



int main() {

  std::vector<int> x{1, 3, 5, 7};

  std::vector<int> y{1, 4};

  std::vector<int> z{3, 4, 10};

  C &c = C::getInstance();

  c.dump();



  foo(x);

  c.dump();

  bar(z);



  foo(y);

  c.dump();

  bar(z);

}

Output

dump:

dump: 1 3 5 7

3 y 4 n 10 n

dump: 1 3 4 5 7

3 y 4 y 10 n