howto count lines - fast

[Nitram via Digitalmars-d-learn]

After reading 
https://dlang.org/blog/2017/05/24/faster-command-line-tools-in-d/ 
, i was wondering how fast one can do a simple "wc -l" in D.

So i made a couple short implementations and found myself 
confronted with slow results compared to "/usr/bin/wc -l".

How would a implementation look like in D, which is fast?