Behavior of signed/unsigned conversion in template parameters

[Peter Alexander]

On 30/07/10 8:52 PM, Peter Alexander wrote:
> Just had this error crop up. I just wanted to check whether this is
> correct behavior as I don't know the details of D's templates. I'm using
> DMD 2.047 to compile with no flags.
>
>
> struct A(uint N) { }
> void b(uint N)() { }
> void c(uint N)(A!(N) a) { }
>
> void main()
> {
> A!(1) a; // OK
> b!(1)(); // OK
> c!(1)(f); // Error - cannot implicitly convert A!(1) to A!(N)
> c(a); // Error - cannot implicitly convert A!(1) to A!(N)
> }
>
>
> Are those errors correct?
>
> If so, why can I instantiate 'A' and 'b' with a signed int parameter,
> but can't instantiate 'c'?
>
> It seems that the uint-ness of the template parameter is only enforced
> when there is an argument involved, but I don't understand the reasoning
> behind this (if any). I would expect either all of these to compile, or
> none to compile.
>
> Thanks in advance.

Oops. If it wasn't obvious, the c!(1)(f) is meant to be c!(1)(a).