Re: [boost] [fusion] Getting rid of the incomplete type error forvector

From: Sebastian Redl (sebastian.redl_at_[hidden])
Date: 2007-10-23 16:16:20

Boris Gubenko wrote:
> For the program below, in strict ansi mode, EDG Front End issues an
> error: "incomplete type is not allowed" (and, accordingly, cxx and aC++
> issue this error also). g++ 4.2.1 does not issue any diagnostics, even
> when compiling '-pedantic -ansi'. Again, I'm not sure if a diagnostics is
> required in this case.
>
> template <typename T>
> struct apply {
>   typedef T type;
> };
>
> template <typename T = void>
> struct vector;
>
> template <typename Iterator>
> static typename apply<Iterator>::type
> call(Iterator)
> {
>     return vector<>();
> }
>   
See 14.6/5:
> No diagnostic shall be issued for a tem-
>   plate definition for which a valid specialization  can  be  generated.
>   If no valid specialization can be generated for a template definition,
>   and that template is not instantiated, it is  unspecified  whether  or
>   not  an implementation is required to issue a diagnostic.
The implementation is allowed to defer issuing a diagnostic until the
function is instantiated.

Sebastian Redl