Re: Asking for trouble with incomplete types?

From:

"John Carson" <jcarson_n_o_sp_am_@netspace.net.au>

Newsgroups:

microsoft.public.vc.language

Date:

Thu, 22 Feb 2007 10:58:25 +1100

Message-ID:

<OFYnARhVHHA.1208@TK2MSFTNGP03.phx.gbl>

"Mark Randall" <markyr@gEEEEEmail.com> wrote in message
news:evkhl2fVHHA.4764@TK2MSFTNGP05.phx.gbl

Hi,

I am trying to reduce the complexity of a set of classes I made a
couple of years ago, what equates to a set of trees, for which I want
to use std::list and avoid having to use direct pointers anywhere.

I wish to have a class contain a list of itself, as so:

class B;
class A
{
public:
std::list<B> List;
typedef std::list<B>::iterator iterator;
iterator begin() { return List.begin(); }
};

class B
{
public:
A m_a;
};

My question is, provided I ensure there is no in class A referencing
direct instances of B, can I be fairly certain im not launching into
a world of c++ driven pain, for example no:

class A
{
...
B GetSomething();
};

I expect that as long as thing that call items such as copy
constructors or -> / * operators of list<B>::iterator are in cpp files
there
should be no issue.

Could anyone tell me different?

As Igor says, the Standard doesn't guarantee that it will work, but it does
currently work with VC++.

Note that class B is unnecessary, e.g., the following works.

class A
{
public:
  A() : x(0)
  {}
  A(int a_x) : x(a_x)
  {}
  std::list<A> List;
  typedef std::list<A>::iterator iterator;
  iterator begin() { return List.begin(); }
  iterator end() { return List.end(); }
  void pushback(const A&arg)
  {
      List.push_back(arg);
  }
  void pop_back()
  {
      List.pop_back();
  }
  int GetValue()
  {return x;}
private:
  int x;
};

int main()
{
    A a(1),b(2),c(3);
    a.pushback(b);
    a.pushback(c);

    cout << a.GetValue() << endl;
    for(A::iterator it = a.begin(); it!=a.end(); ++it)
        cout << it->GetValue() << endl;

    return 0;
}

--
John Carson