Why can't enums be used as types in this (simplified) example?

enum Positivity
{
	Positive,
	Negative
}

struct Wave
{
public:
	Positivity slope;
}

enum Waves
{
	Sin = Wave(Positivity.Positive),
	Cos = Wave(Positivity.Negative)
}

int nth_value(T : Waves)(int n);

int nth_value(T : Waves.Sin)(int n)
{
	return n % 2 ? 1 : -1;
}

int nth_value(T : Waves.Cos)(int n)
{
	return n % 2 ? -1 : 1;
}

void main()
{
	import std.stdio;

	writeln(nth_value!(Waves.Sin)(1));
}

On Monday, 4 December 2017 at 22:34:41 UTC, helxi wrote:
> enum Waves
> {
> 	Sin = Wave(Positivity.Positive),
> 	Cos = Wave(Positivity.Negative)
> }
> 	writeln(nth_value!(Waves.Sin)(1));
> }

Sin and Cos there are actually values, not types...

On Monday, 4 December 2017 at 22:34:41 UTC, helxi wrote:
> Why can't enums be used as types in this (simplified) example?
>
> enum Positivity
> {
> 	Positive,
> 	Negative
> }
>
> struct Wave
> {
> public:
> 	Positivity slope;
> }
>
> enum Waves
> {
> 	Sin = Wave(Positivity.Positive),
> 	Cos = Wave(Positivity.Negative)
> }
>
> int nth_value(T : Waves)(int n);
>
> int nth_value(T : Waves.Sin)(int n)
> {
> 	return n % 2 ? 1 : -1;
> }
>
> int nth_value(T : Waves.Cos)(int n)
> {
> 	return n % 2 ? -1 : 1;
> }

We Adam said, Waves.Sin and Waves.Cos are values, while Waves itself is the type. You want to do the following:

int nth_value(Waves w: Waves.Sin)(int n)
{
    //Etc.
}

At least I *think* that's what you want. I'm on mobile and dpaste is down so I have no way to double check the syntax, which I can never remember.