Returning an empty range of a given type

[Idan Arye via Digitalmars-d-learn]

On Thursday, 14 May 2015 at 12:40:57 UTC, rcorre wrote:
> So I thought this might work:
>
> struct MaybeEmpty(R) if (isInputRange!R) {
>   private bool _isEmpty;
>   private R    _input;
>
>   alias _input this;
>
>   this(bool isEmpty, R input) {
>     _input = input;
>     _isEmpty = isEmpty;
>   }
>
>   @property bool empty() {
>     return _isEmpty || _input.empty;
>   }
> }
>
> auto maybeEmpty(R)(bool empty, R input = R.init) if 
> (isInputRange!R) {
>   return MaybeEmpty!R(empty, input);
> }
>
> It's kind of ugly, but it can be used like:
>
>   auto a = maybeEmpty!MyRange(true);
>   auto b = maybeEmpty!MyRange(false, actualRange);
>   static assert(is(typeof(a) == typeof(b)));
>
> However, it fails the input range test:
>
> static assert(isInputRange!MyRange); //pass
> static assert(isInputRange!(typeof(a))); // fail
>
> But it seems to be something weird with cross-module template 
> instantiation. If I replace `import std.range` with a 
> copy-paste of `isInputRange`, the above passes.
>
> Either that or I'm doing something stupid because I'vebeen 
> staring at this too long.
>
> I'm wondering if the isInputRange thing is a bug, so here's a 
> gist if anyone wants to play with it:
> https://gist.github.com/rcorre/7a62395c53baf3c0bfbc

How about a more flexible solution?

http://dpaste.dzfl.pl/2f99cc270651