Check template parameter whether it has "length"

[John Colvin via Digitalmars-d-learn]

On Thursday, 8 October 2015 at 15:22:02 UTC, tcak wrote:
> BTW, there is nothing like std.traits.hasLength.

yeah, that's because __traits(hasMember, ...) should be good 
enough, but obviously not in this case at the moment.