Re: [boost] [type_at] Variadic template utility

Subject: Re: [boost] [type_at] Variadic template utility
From: Johannes Schaub (litb) (schaub.johannes_at_[hidden])
Date: 2011-05-27 07:30:18

Mathias Gaunard wrote:

> On 26/05/2011 13:19, Larry Evans wrote:
>> On 05/26/11 04:47, tymofey wrote:
>>>> Robert Jones<robertgbjones_at_[hidden]>
>>>> On Thu, May 26, 2011 at 8:34 AM, tymofey<tymofey_at_[hidden]>  wrote:
>>>>
...
> You cannot expand a template parameter pack to instantiate a
> non-variadic template.
> 
> Typically, this
> 
> template<typename... T>
> struct make_vector
> {
>      typedef boost::mpl::vector<T...> type;
> }:
> 
> doesn't work.
> 
> GCC gives the error:
> sorry, unimplemented: cannot expand 'T ...' into a fixed-length argument
> list
> 
> And I believe the standard doesn't require it just because it would be
> difficult to implement in GCC's codebase.

My understanding is that the spec requires this to be well-formed code. 
Clang doesn't currently accept it, and I made a PR against it some time ago: 
http://llvm.org/bugs/show_bug.cgi?id=9021