Re: How to detect const reference to temporary issues at compile or runtime?

=?ISO-8859-1?Q?Daniel_Kr=FCgler?= <>
Thu, 2 Dec 2010 06:11:51 CST
On 12/2/2010 02:54, Dragan Milenkovic wrote:

On 12/01/2010 01:26 PM, Daniel Kr?gler wrote:

On 12/1/2010 04:07, Clinton Mead wrote:

Hi All

I've found recently that most of the errors in my C++ programs are of
a form like the following example:


class Z
Z(int n) : n(n) {}
int n;

class Y
Y(const Z& z) : z(z) {}
const Z& z;

In C++0x you could add the following deleted constructor

Y(const Z&&) = delete;

to prevent rvalues to bind to the first constructor.

I like that! Although, I would opted for Y(const Z * z)
or maybe a smart pointer parameter and would document
that the instance of Z must outlive the instance of Y.

And about such code being in a 3rd party library, how about
making a wrapper?

Y make_Y(const Z * z) { return Y(*z); }

... or use Daniel's suggestion on make_Y.

In fact the new C++0x library follows a similar approach in regard to
the class template reference_wrapper (which is quite similar to class Y

template <class T> reference_wrapper<T> ref(T&);
template <class T> reference_wrapper<const T> cref(const T&);
template <class T> void ref(const T&&) = delete;
template <class T> void cref(const T&&) = delete;
template <class T> reference_wrapper<T> ref(reference_wrapper<T>);
template <class T> reference_wrapper<const T> cref(reference_wrapper<T>);

and the class template synopsis:

template <class T> class reference_wrapper
public :
   // construct/copy/destroy
   reference_wrapper(T&&) = delete; // do not bind to temporary objects
   reference_wrapper(const reference_wrapper<T>& x);

HTH & Greetings from Bremen,

- Daniel Kr?gler

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