Ggthjy

This is an implementation to simulate the basic functionality of c++ shared_ptr.
This doesn't provide features like custom deleter and make_shared().

I would really appreciate any feedback to improve the below code, any other api's that I should be providing etc.

#ifndef SHARED_PTR_H_

#define SHARED_PTR_H_



#include <utility>



namespace kapil {

  template <typename T>

  class shared_ptr {

    private:

      T* ptr_;   // data pointer

      int* ref_count_;  // reference count pointer



      void decrement_ref_count_and_delete_if_needed() {

        if (ref_count_) {

          --(*ref_count_);

            if (*ref_count_ == 0) {

              delete ptr_;

              delete ref_count_;

              ptr_ = nullptr;

              ref_count_ = nullptr;

            }

        }

      }



    public:

      constexpr shared_ptr() noexcept : ptr_{nullptr}, ref_count_{nullptr} {}



      constexpr explicit shared_ptr(T* ptr) {                  // constructor

        ptr_ = ptr;

        ref_count_ = new int{1};

      }



      shared_ptr(const shared_ptr& other) noexcept { // copy constructor

        ptr_ = other.ptr_;

        ref_count_ = other.ref_count_;

        if (ref_count_ != nullptr) {

          ++(*ref_count_);

        }

      }



      shared_ptr(shared_ptr&& other) noexcept {  // move constructor

        ptr_ = other.ptr_;

        ref_count_ = other.ref_count_;

        other.ptr_ = nullptr;

        other.ref_count_ = nullptr;

      }



      ~shared_ptr() noexcept {             // destructor

        decrement_ref_count_and_delete_if_needed();

      }



      shared_ptr& operator = (const shared_ptr& other) noexcept {   // assignent operator

        if (this != &other) {

          decrement_ref_count_and_delete_if_needed();

          ptr_ = other.ptr_;

          ref_count_ = other.ref_count_;

          if (ref_count_) {

            ++(*ref_count_);

          }

        }

        return *this;

      }



      shared_ptr& operator = (shared_ptr&& other) noexcept {   // move assignment operator

        *this = other;

      }



      T* get() const noexcept {

        return ptr_;

      }



      void reset() noexcept {

        decrement_ref_count_and_delete_if_needed();

      }



      void reset(T* ptr) {

        decrement_ref_count_and_delete_if_needed();

        ptr_ = ptr;

        if (!ref_count_) {

          ref_count_ = new int{1};

        }

        *ref_count_ = 1;

      }



      int use_count() const noexcept {

        return *ref_count_;

      }



      void swap (shared_ptr& other) {

        std::swap(ptr_, other.ptr_);

        std::swap(ref_count_, other.ref_count_);

      }



      T& operator * () const {

        return *ptr_;

      }



      T* operator -> () const noexcept {

        return ptr_;

      }



      explicit operator bool() const noexcept {

        return (ptr_ != nullptr);

      }



      friend bool operator == (const shared_ptr& lhs, const shared_ptr& rhs) noexcept {

        return (lhs.ptr_ == rhs.ptr_);

      }



      friend bool operator != (const shared_ptr& lhs, const shared_ptr& rhs) noexcept {

        return !(lhs == rhs);

      }

  }; // class shared_ptr



  template <typename T>

  void swap(shared_ptr<T>& lhs, shared_ptr<T>& rhs) {   // swap function in namespace to facilitate ADL

    lhs.swap(rhs);

  }

} // namespace kapil



#endif