small exercise :-)

Hi

Here is the small problem that looks quite hard to crack. Task is to
compile code below without using operator== that takes C by value.

Basically -- I've been trying to implement something similar to C#
accessors. Initial plan was to make them as 'undetectable' as possible
-- i.e. moving from exposed data member to accessors (and backwards)
should not require client code change (not taking '()' into account
however).
But it looks like that C++ rules does not allow to create such object.
For example, code below compiles if you use second A::data()
declaration.

template<class T>
class accessor
{
    T& m_ref;

    typedef accessor<T> Self;
    template<class T> friend inline accessor<T> make_accessor(T& d)
{ return accessor<T>(d); }

    accessor();
    accessor(T& ref) : m_ref(ref) {}
public:
    // compiler generated cctor & dtor are ok

    template<class C> inline operator C() { return m_ref; }

    // operator==
    template<class C> friend inline bool operator==(Self l, C const&
r) { return l.m_ref == r; }
    template<class C> friend inline bool operator==(C const& l, Self
r) { return l == r.m_ref; }
    friend inline bool operator==(Self l, Self r) { return l.m_ref ==
r.m_ref; }
};

struct B
{
    int k;

    B(int a = 0) : k(a) {}
    operator int() {return k;} // no const deliberately!

    //friend inline bool operator==(B const& l, B const& r) { return
l.k == r.k; }
    //bool operator==(B const& r) const { return k == r.k; }
};

class A
{
    B m_data;
public:
    A(int d) : m_data(d) {}

    accessor<B> data() throw() { return make_accessor(m_data); }
    //B& data() throw() { return m_data; }
};

main()
{
    bool volatile bval;
    A a1(1);
    A a2(2);
    B b;

    bval = a1.data() == a2.data();
    bval = A(3).data() == a2.data();
    bval = a1.data() == A(3).data();
    bval = b == a2.data();
    bval = a1.data() == b;
    bval = 5 == a2.data();
    bval = a1.data() == 5;
    bval = a1.data() == B();
    bval = B() == a2.data();

    int aa = a1.data();
}

Bye.
Sincerely yours, Michael.

--
      [ See http://www.gotw.ca/resources/clcm.htm for info about ]
      [ comp.lang.c++.moderated. First time posters: Do this! ]