Wait, I missed a contradiction here.

On Wednesday 20 September 2017 09:30 AM, Junio C Hamano wrote:

....  And !!ptr is a shorter and more established way than ptr
!= NULL to turn non-NULL ness into an int boolean,

Documentation/SubmittingPatches says:

 - Some clever tricks, like using the !! operator with arithmetic
   constructs, can be extremely confusing to others.

If !!ptr is a **more established way** to then why should it confuse 
others. Of course,
!!ptr was stated as an "exception-rule" where ptr is a pointer (possibly 
NULL). That makes
me wonder in what case is it "confusing" at all?

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Kaartic