More fun with autodecoding

[Nick Sabalausky (Abscissa)]

On 09/11/2018 09:06 AM, Steven Schveighoffer wrote:
> 
> Then I found the true culprit was isForwardRange!R. This led me to 
> requestion my sanity, and finally realized I forgot the empty function.

This is one reason template-based interfaces like ranges should be 
required to declare themselves as deliberately implementing said 
interface. Sure, we can tell people they should always `static 
assert(isForwardRage!MyType)`, but that's coding by convention and 
clearly isn't always going to happen.