Re: [boost] [type_traits][parameter] Inconsistent boost::is_convertible between gcc and clang

Subject: Re: [boost] [type_traits][parameter] Inconsistent boost::is_convertible between gcc and clang
From: John Maddock (boost.regex_at_[hidden])
Date: 2012-08-18 03:41:09

>> The following code works well (incl. your mentioned cases)
>> both in C++03 and C++11 on gcc.
> <snip>
>>     static bool const rval_to_nonconst_lval_ref_conv = 
>> ::boost::type_traits::ice_and<
>>         !(::boost::is_function<From>::value) // Note: an rvalue ref to 
>> function type is an lvalue
>>       , !(::boost::is_reference<From>::value)
>>       , ::boost::is_reference<To>::value
>>       , !(::boost::is_const<typename 
>> ::boost::remove_reference<To>::type>::value)
>>     >::value;
>
> Sorry, the above code is wrong. It does not detect binding
> const volatile reference to an rvalue.
> Here is a right code:
>
>    static bool const rval_to_nonconst_lval_ref_conv =
> ::boost::type_traits::ice_and<
>        !(::boost::is_function<From>::value) // Note: an rvalue ref to
> function type is an lvalue
>      , !(::boost::is_reference<From>::value)
>      , ::boost::is_reference<To>::value
>      , ::boost::type_traits::ice_or<
>            !::boost::is_const<typename
> ::boost::remove_reference<To>::type>::value
>          , ::boost::type_traits::ice_and<
>                ::boost::is_const<typename
> ::boost::remove_reference<To>::type>::value
>              , ::boost::is_volatile<typename
> ::boost::remove_reference<To>::type>::value
>            >::value
>        >::value
>    >::value;

Michel,

Apologies for the delay, as I have no time right now, can you please let me 
have this as a patch, and verify our test suite passes?  Any changes should 
also probably be dependent upon BOOST_NO_SFINAE_EXPR as well as I believe 
the technique depends upon that.

Sorry for the abundance of caution, but something somewhere usually breaks 
when we mess with a header like that, and there's a limit to how many folks 
I'm willing to annoy to fix a corner case! ;-)

Cheers, John.