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: John Maddock (boost.regex_at_[hidden])
Date: 2011-02-04 04:25:32

> 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'm not sure if that's still an issue for current compilers, but the 
workaround would be:

template <class T, bool b>
struct bar{ /*actual implementation here*/ };

template <class T>
struct foo : public bar<T, ::boost::is_integral<T>::value> {}

HTH, John.