path: root/third_party/nix/src/libutil/ref.hh

#pragma once

#include <exception>
#include <memory>
#include <stdexcept>

namespace nix {

/* A simple non-nullable reference-counted pointer. Actually a wrapper
   around std::shared_ptr that prevents non-null constructions. */
template <typename T>
class ref {
 private:
  std::shared_ptr<T> p;

 public:
  ref<T>(const ref<T>& r) : p(r.p) {}

  explicit ref<T>(const std::shared_ptr<T>& p) : p(p) {
    if (!p) {
      throw std::invalid_argument("null pointer cast to ref");
    }
  }

  explicit ref<T>(T* p) : p(p) {
    if (!p) {
      throw std::invalid_argument("null pointer cast to ref");
    }
  }

  T* operator->() const { return &*p; }

  T& operator*() const { return *p; }

  operator std::shared_ptr<T>() const { return p; }

  std::shared_ptr<T> get_ptr() const { return p; }

  template <typename T2>
  ref<T2> cast() const {
    return ref<T2>(std::dynamic_pointer_cast<T2>(p));
  }

  template <typename T2>
  std::shared_ptr<T2> dynamic_pointer_cast() const {
    return std::dynamic_pointer_cast<T2>(p);
  }

  template <typename T2>
  operator ref<T2>() const {
    return ref<T2>((std::shared_ptr<T2>)p);
  }

 private:
  template <typename T2, typename... Args>
  friend ref<T2> make_ref(Args&&... args);
};

template <typename T, typename... Args>
inline ref<T> make_ref(Args&&... args) {
  auto p = std::make_shared<T>(std::forward<Args>(args)...);
  return ref<T>(p);
}

}  // namespace nix