Re: [Gluster-devel] !! operator

[Emmanuel Dreyfus]

Jeff Darcy  wrote:

> Sorry if my comment came off as dismissive.

It was not dissmissive. My reply was not ironic, I was gladly surprised
to learn something about C syntax.

>From an objective code-readability standpoint it's probably a bad
> idiom. 

IMO the root of the problem is the lack of a built-in boolean type in C,
but that is not big business.

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Emmanuel Dreyfus
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m...@netbsd.org
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Re: [Gluster-devel] !! operator

[Jeff Darcy]

> Thanks for the explanation. I was able to practice C for 18 years in
> numerous projects without having the opportunity to see it. I will got
> to bed less ignorant tonight. :-)

Sorry if my comment came off as dismissive.  I was only trying to
explain why I'd assume it's intentional.  I'll readily admit that
I had the exact same reaction when I first saw this construct.
>From an objective code-readability standpoint it's probably a bad
idiom.  While it is definitely concise, the syntax gives no hint
as to its intent, and it's often unnecessary.  This and the dozen
other instances of !! in our code should probably be eliminated
or replaced with a macro.  TO_BOOLEAN, perhaps?
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Re: [Gluster-devel] !! operator

[Emmanuel Dreyfus]

Jeff Darcy  wrote:

> It's a common idiom in the Linux kernel/coreutils community.  I
> thought it was in BSD too.

Thanks for the explanation. I was able to practice C for 18 years in
numerous projects without having the opportunity to see it. I will got
to bed less ignorant tonight. :-)

-- 
Emmanuel Dreyfus
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m...@netbsd.org
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Re: [Gluster-devel] !! operator

[Jeff Darcy]

> I found a !! in glusterfs sources. Is it a C syntax I do not know, a
> bug, or just a weird syntax?
> 
> xlators/cluster/afr/src/afr-inode-write.c:
>  local->stable_write = !!((fd->flags|flags)&(O_SYNC|O_DSYNC));

It's a common idiom in the Linux kernel/coreutils community.  I
thought it was in BSD too.  It's a convenient way to coerce any
arbitrary non-zero integer value into a specific value of one,
for code that uses integers as booleans.  I wouldn't assume it's
a bug, since that seems to be precisely what's called for in the
snippet you provided, but I guess that means it's weird syntax.
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