Template alias parameter: error: need 'this' for ...

[Paul Backus]

On Friday, 24 February 2023 at 14:22:17 UTC, user1234 wrote:
> you can break using `goto`, restore `static` everywhere, and 
> using local introspection determine whether the result exists.
>
> ```d
> struct Bar
> {
> 	@("hello") int t;
> }
>
> static bool hasAttribute(alias F, T)()
> {
> 	static foreach (a; __traits(getAttributes, F))
> 	{
> 		static if (is(typeof(a) : T))
> 		{
> 			enum result = true;
> 			goto L0;
> 		}
> 	}
> 	L0:
> 	static if (is(typeof(result)))
> 		return result;
> 	else
> 		return false;
> }
>
> void main()
> {
> 	import std.stdio;
>
> 	writeln(hasAttribute!(Bar.t, string));
> }
> ```

Unfortunately there is a serious bug in this code. Take a look at 
what happens when you try it with this `struct Bar`:

```d
struct Bar
{
	@("hello") @("goodbye") int t;
}
```