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From: John Maddock (john_at_[hidden])
Date: 2007-01-22 05:16:04


Daniel Wallin wrote:
> John Maddock wrote:
>> Dmitry Ivankov wrote:
>>> Doesn't work for void operator*(B&), but can we call such class
>>> dereferencable? :)
>>
>> No, I think there will always be some corner cases like that where
>> it blows up, but does anyone really write such an operator in
>> practice?
>
> It's quite possible to handle the case where *x is void. See for
> example boost/detail/is_incrementable.hpp. A couple of years ago, I
> tried to generalize this into something reusable and more powerful.
> The result of that is available in the sandbox;
> boost/result_check.hpp. The intended usage was something like:
>
> BOOST_RESULT_CHECK(1, operator*, dereference, *_1)
> ^ ^ ^ ^
> arity ----' | | |
> function -' | |
> metafunction name -' |
> operation -'
>
> template <class T>
> struct is_dereferencable
> : check_dereference<T>
> {};
>
> template <class T>
> struct is_dereference_void
> : check_dereference<T, boost::is_void<mpl::_> >
> {};
>
> template <class T, class U>
> struct is_dereference_convertible_to
> : check_dereference<T, boost::is_convertible<mpl::_, U> >
> {};

Very interesting, I've had a play with that, and it does indeed seem to be a
superior solution.

Thanks!

John.


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