Given that overall reaction is positive, I'll make the change, starting with the 'cast to reference' logic I wanted in the first place.
The only difference between my version and the one you mention above is this snippet in 'any_cast':
#ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION // Please use BOOST_BROKEN_COMPILER_TYPE_TRAITS_SPECIALIZATION macro // to generate specialization of remove_reference for your class // See type traits library documentation for details BOOST_STATIC_ASSERT(!::boost::is_reference<nonref>::value); #endif
It looks to me that this assert will always be triggered when your
Vladimir Prus wrote: pass
reference type and BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION is defined, right? The assert will fire even if used has specialized remove_reference, no? If that's true, the comment is not correct and casting to reference is just not supported for broken compilers.
On broken compilers the assert for any_cast<int cv&> fires only if this thing is not in TU before first use of any_cast<int v&>: BOOST_BROKEN_COMPILER_TYPE_TRAITS_SPECIALIZATION(int) IMHO, if it's there, everything should work. BTW, there is a testcase in my earlier post in that thread. You can try to comment one such workaround to see the difference on a broken compiler or with BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION defined. Be careful, don't mix up the correct patch with previous version that comes with the test.
I see that your patch also: 1. Strips cv-qualification in constructor (which is reasonable).
const is already stripped because ctor's argument is 'const ValueType & value'. So, it's only for volatile. remove_cv is used only to avoid inclusion of remove_volatile.hpp.
2. Strips cv-qualification when casting to pointer.
Why the second aspect is needed?
I forgot to mention that the original version has small problem with any_cast to const type. If any stores T and you cast it to T const you're
Quoting myself: trying
this sequence of static_casts:
holder<T>* -> (in ctor) -> placeholder* -> (in any_cast) -> holder<T> const>*
Obviously, it's not getting back to original holder<T> type.
-- Alexander Nasonov