From: Junio C Hamano <gitster@pobox.com>
Date: Thu, 21 Sep 2017 01:31:56 GMT
Subject: Re: [RFC PATCH 1/5] builtin/checkout: avoid usage of '!!'
Message-ID: <xmqqlgl8n8fn.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <fbe3d3e2-a14c-fe7c-7e5d-c24789b249ca@gmail.com>

Kaartic Sivaraam <kaarticsivaraam91196@gmail.com> writes:

> Wait, I missed a contradiction here.
> ..
> Documentation/SubmittingPatches says:
>
>>  - Some clever tricks, like using the !! operator with arithmetic
>>    constructs, can be extremely confusing to others.

What does "with arithmetic constructs" mean?  Would it refer to
things like

	!!i != !!(j + 3)

that unnecessarily obfuscates what is going on?

The primary reason why !!ptr is good in the code that this patch
touches is because what is doubly negated is a pointer, not an
integer or other things.  The called function does *not* limit its
input to 0 or 1 (it wants 0 for false and everything else for true),
so we wouldn't be doing !!i if what we are passing is already an
integer.  But we cannot just pass a pointer to such a parameter
without getting the compiler upset.