isInputRange copied verbatim produces a different result than isInputRange from std.range

[Adam D. Ruppe]

On Sunday, 4 March 2018 at 12:57:41 UTC, aliak wrote:
> @property int front(D d) { return 2; }
> @property bool empty(D d) { return false; }
> void popFront(D d) {}

Those functions are in scope for your function, but not inside 
std.range.

in other words std.range hasn't imported your module, so it can't 
see those three functions.