Re: [boost] [type_traits] extension has_operator_xxx - conforming to coding guidelines for ICE

Subject: Re: [boost] [type_traits] extension has_operator_xxx - conforming to coding guidelines for ICE
From: Jeffrey Lee Hellrung, Jr. (jhellrung_at_[hidden])
Date: 2011-02-03 18:01:49

On 2/3/2011 2:36 PM, Frédéric Bron wrote:
> I have tried to comply with the coding guidelines for integral
> constant expressions
> (http://www.boost.org/development/int_const_guidelines.html).
> I have been able to comply with most of them but still have the following issue:
>
>> Don't use dependent default parameters for non-type template parameters.
>> For example:
>>
>> template<class T, int I = ::boost::is_integral<T>::value>   // Error can't deduce value of I in some cases.
>> struct foobar;
>>
>> Rationale: this kind of usage fails for Borland C++. Note that this is only an issue where the default value is dependent upon a previous template parameter, for example the following is fine:
>
> Is there any known workaround for this? In my case, int is replaced by
> bool but I think it is the same issue.

I don't know if the following is an improvement, but...

template<
     class T,
     class I = boost::integral_constant<
                   int,
                   boost::is_integral<T>::value
               >
 >
struct foobar;

template< class T >
struct foobar< T, boost::integral_constant< int, 0 > >
{ ... };

(Alternatively, use boost::mpl::int_ (and its ilk).)

- Jeff