Anyone know what's going on here? (variable with an instantiated template as a type shows up as void when instantiating another template)

[Robert Jacques]

On Fri, 23 Apr 2010 10:25:35 -0300, Gareth Charnock <gareth at oerc.ox.ac.uk>  
wrote:
> Is this a bug, or am I being dense? I've tried it this on 2.036,2.042  
> and 2.043 and on each the compiler produces errors. Searched bugzilla  
> for "template and instantiated" and "template and instantiate"
>
> struct A(uint N)  {
> }
> void unary_op(uint N)(A!(N)) {
> }
> void main() {
>      A!(3) a3;
>
>      pragma(msg,typeof(a3)); //prints A!(3), so a3 is not void, dammit
>
>      unary_op!3(A);// Error: cannot implicitly convert expression
>                    // (A(uint N)) of type void to A!(N)
>      unary_op(A);  // Error: template template.unary_op(uint N) does not  
>                    // match any function template declaration
>                    // Error: template template.unary_op(uint N) cannot
>                    // deduce template function from argument types
>                    // !()(void)   <== what?
> }

Well, first, let's make this valid D code:


struct A(uint N)  {}

void unary_op(uint N)(A!N value) {}

void main(string[] args) {
     A!(3) a3;
     pragma(msg,typeof(a3));
     unary_op!3(a3);
     unary_op(a3);
}

But that still doesn't compile.

It looks like you're running across a variant of bug 2257  
(http://d.puremagic.com/issues/show_bug.cgi?id=2257). Please vote it up.