Re: class in class

From:

cbarron3@ix.netcom.com (Carl Barron)

Newsgroups:

comp.lang.c++.moderated

Date:

Sun, 1 Jul 2007 05:45:06 CST

Message-ID:

<1i0ixsj.k2h8zt1ht6u56N%cbarron3@ix.netcom.com>

Seungbeom Kim <musiphil@bawi.org> wrote:

You can create the mapping explicitly:

struct A
{
     struct C
     {
         C(A& a) : parent_(a) { }
         A& parent_;
     } c;
     A() : c(*this) { }
};

Now the C object contains a reference to an A object (supposedly the one
that contains it), and the A object initializes its c sub-object by
giving it the reference to itself.

   A couple of small thoughts:
   Using a pointer keeps A copyable and assignable without change if it
was originally. It also keeps A::C copyable and assignable if it was.
Further if conversion from A::C to A can safely be done implicitly.
[It appears so] then operator A &() const; is a one liner. Const
because the conversion does not modify A::C. Then getting reference
from the object c, is simply

    A::C t = ...;
    A &a = t;
    or even
    void foo(A &a);

    foo(t); as long as foo is not a templated function.

class A::C
{
    A *parent_;
public:
    C (const A &a):parent_(&a){}
    operator A & () const {return *parent_;}
    // ...
};
comes to mind. [looks a lot like a reference wrapper like provided by
boost and tr1].

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