E0213: A declarer can't take this declaration

A declarer (a decorator of type func(*vuka.Decl)) or a registry decorator (@web.Get) registers the function it decorates, so it needs one it can refer to: not generic, not init, and for a declarer a function, not a type (a type's declarer takes a *vuka.Type).

Wrong

@register
func first[T any](xs []T) T { return xs[0] }

Right

@register
func firstInt(xs []int) int { return xs[0] }