Re: [RFC PATCH 1/5] builtin/checkout: avoid usage of '!!'

From: Junio C Hamano <gitster@pobox.com>
Date: Sep 21, 2017, 01:31 UTC
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:

Show 6 quoted lines

> 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.