I found that extern( foo ) instance .... did not migrate the linkage to the
template
so not wanting to use an enum, first I tried template( char[] T : "Windows",
R )
but that does not work :(
tet5.d(2): template base(char[] : "W",R) integral type expected for
value-parame
ter, not char[]

then I tried this

template base( char T : 'W', R )
{
 extern (Windows) alias R (*fp)();
 fp func;
}

template base( char T : 'C', R )
{
 extern (C) alias R (*fp)();
 fp func;
}

const char WWWW = 'W';
instance base( WWWW, int ) other;
instance base( 'W', int ) te;
extern( Windows ) alias int (*wfp)();
extern( Windows ) alias te.fp awfp;

int myd_func(){ return 2; }

int main( char[][] args )
{
 wfp wfunc;
 awfp awfunc;
 awfunc = &myd_func;
 te.func = &myd_func;
 wfunc = &myd_func; // only windows fp
 return 0;
}

the templates compile .... BUT
there is no way to create an instance on them

instance base("W",int) does not match any template declaration

with both 'W' or a const

Mike.

"Mike Wynn" <mike.wynn@l8night.co.uk> wrote in message news:b245qp$1eud$1@digitaldaemon.com...
> I found that extern( foo ) instance .... did not migrate the linkage to
the
> template

Right. It compiles the template in the context it was defined in, not the context of the instance.

> so not wanting to use an enum, first I tried template( char[] T :
"Windows",
> R )
> but that does not work :(
> tet5.d(2): template base(char[] : "W",R) integral type expected for
> value-parame
> ter, not char[]

Right, only integral values supported for value parameters.

> then I tried this
>
> template base( char T : 'W', R )
> {
>  extern (Windows) alias R (*fp)();
>  fp func;
> }
>
> template base( char T : 'C', R )
> {
>  extern (C) alias R (*fp)();
>  fp func;
> }
>
> const char WWWW = 'W';
> instance base( WWWW, int ) other;
> instance base( 'W', int ) te;
> extern( Windows ) alias int (*wfp)();
> extern( Windows ) alias te.fp awfp;
>
> int myd_func(){ return 2; }
>
> int main( char[][] args )
> {
>  wfp wfunc;
>  awfp awfunc;
>  awfunc = &myd_func;
>  te.func = &myd_func;
>  wfunc = &myd_func; // only windows fp
>  return 0;
> }
>
> the templates compile .... BUT
> there is no way to create an instance on them
>
> instance base("W",int) does not match any template declaration
>
> with both 'W' or a const

I'll log that as a compiler bug.