Re: Using std::pair<T1,T2> with ABC interfaces

On 26 Nov., 01:00, Andrey Vul wrote:


Not really. You need a pointer *somewhere*. There are a couple of
options and the right one depends on what you're actually trying to
do:

  - raw pointer
  - shared_ptr (Boost or TR1 or C++0x)
  - unique_ptr (C++0x)
  - some kind of "value semantics"-emulating wrapper
    (similar to a unique_ptr but calls Base::clone on copy)

  template<class Base>
  class polyvalue
  {
  public:
    /// takes ownership, will call delete on the pointer
    explicit polyvalue(Base* p=0)
    : ptr_(p)
    {}

    /// creates a new copy via the clone member function
    polyvalue(polyvalue const& x)
    : ptr_(x.ptr_ ? x.ptr_->clone() : 0)
    {}

    ~polyvalue()
    { delete ptr_; }

    void swap(polyvalue & that)
    { std::swap(this->ptr_,that.ptr_); }

    friend void swap(polyvalue & a, polyvalue & b)
    { a.swap(b); }

    polyvalue& operator=(polyvalue tmp)
    { tmp.swap(*this); return *this; }

    Base const& operator*() const { return ptr_; }
    Base & operator*() { return ptr_; }
    Base const* operator->() const { return ptr_; }
    Base * operator->() { return ptr_; }
    Base const* get() const { return ptr_; }
    Base * get() { return ptr_; }
  private:
    Base* ptr_;
  };

(untested)

Cheers!
SG