Is returning a const& valid?

Hi

I have run into a problem regarding references to temporary objects.
I solved the problem by
returning a const reference to the temporary object, this feels very
wrong to me.

I have been using Blitz++ Arrays, one aspect i dislike is that
assignment to an uninitialised
blitz::Array copies 0 elements.

I wrote a proxy class whose operator= references the source array
instead of copying elements.

template<typename T, int N>
class blitz_array_proxy
{
public:
   blitz_array_proxy(blitz::Array<T, N>& ar)
     : ar_(ar) { }

   blitz_array_proxy& operator=(const blitz::Array<T, N>& ar)
   {
     ar_.reference(ar);
     return *this;
   }

private:
   // Silence level 4 warning in Visual C++ 2005
   blitz_array_proxy& operator=(const blitz_array_proxy& bap);

   blitz::Array<T, N>& ar_;
};

and a helper function to deduce template types,

template<typename T, int N>
blitz_array_proxy<T, N> init(blitz::Array<T, N>& ar)
{
    return blitz_array_proxy<T, N>(ar);
}

This can be used as follows,

Array<double, 1> a(6);
Array<double, 1> b;

b = a; // Copies 0 elements
init(b) = a; // Equivalent to b.reference(a);

I ran into a problem when I tried to combine this with Boost Tuple as
I wish to return
multiple blitz::Arrays from a function. The problem is that tuples'
tie function takes
its parameters as references in order to alter them,

tie(init(b)) = make_tuple(a); // Compile Error - reference to
temporary

I found that I could work around this by altering blitz_array_proxy's
operator= to,

const blitz_array_proxy& operator=(const blitz::Array<T, N>& ar) const
{
   ar_.reference(ar);
   return *this;
}

and changing the helper function as follows,

template<typename T, int N>
const blitz_array_proxy<T, N>& init(blitz::Array<T, N>& ar)
{
   const blitz_array_proxy<T, N>& r = blitz_array_proxy<T, N>(ar);
   return r;
}

This allows the program to compile and run successfully, it has also
worked with multiple
element tuples. I've only been able to try this on Visual C++ 2005.
Is the code valid?
Is there an alternative solution?

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