[Any implementation in cpp] #any #cpp

some.h

class Some {

  template <typename T> struct type {
    static void id() {}
  };

  template <typename T> static size_t type_id() {
    return reinterpret_cast<size_t>(&type<T>::id);
  }

  template <typename T> using decay = typename std::decay<T>::type;

  template <typename T>
  using none = typename std::enable_if<!std::is_same<Some, T>::value>::type;

  struct base {
    virtual ~base() {}
    virtual bool is(size_t) const = 0;
    virtual base *copy() const = 0;
  } *p = nullptr;

  template <typename T> struct data : base, std::tuple<T> {
    using std::tuple<T>::tuple;

    T &get() & { return std::get<0>(*this); }
    T const &get() const & { return std::get<0>(*this); }

    bool is(size_t i) const override { return i == type_id<T>(); }
    base *copy() const override { return new data{get()}; }
  };

  template <typename T> T &stat() { return static_cast<data<T> &>(*p).get(); }

  template <typename T> T const &stat() const {
    return static_cast<data<T> const &>(*p).get();
  }

  template <typename T> T &dyn() { return dynamic_cast<data<T> &>(*p).get(); }

  template <typename T> T const &dyn() const {
    return dynamic_cast<data<T> const &>(*p).get();
  }

  size_t size_ = 0;

public:
  Some() {}
  ~Some() { delete p; }

  Some(Some &&s) : p{s.p} {
    s.p = nullptr;
    size_ = s.size();
  }
  Some(Some const &s) : p{s.p->copy()} {}

  template <typename T, typename U = decay<T>, typename = none<U>>
  Some(T &&x) : p{new data<U>{std::forward<T>(x)}} {
    size_ = sizeof(U);
  }

  Some &operator=(Some s) {
    swap(*this, s);
    return *this;
  }

  friend void swap(Some &s, Some &r) { std::swap(s.p, r.p); }

  void clear() {
    delete p;
    p = nullptr;
  }

  bool empty() const { return p; }

  template <typename T> bool is() const {
    return p ? p->is(type_id<T>()) : false;
  }

  size_t size() const { return size_;}

  template <typename T> T &&get() && { return std::move(stat<T>()); }
  template <typename T> T &get() & { return stat<T>(); }
  template <typename T> T const &get() const & { return stat<T>(); }

  template <typename T> T &&cast() && { return std::move(dyn<T>()); }
  template <typename T> T &cast() & { return dyn<T>(); }
  template <typename T> T const &cast() const & { return dyn<T>(); }

  template <typename T> operator T &&() && { return std::move(get<T>()); }
  template <typename T> operator T &() & { return get<T>(); }
  template <typename T> operator T const &() const & { return get<T>(); }
};