Re: (0 == foo), rather than (foo == 0)

[Peter Williams <peterw@aurema.com>]

Linus Torvalds wrote:
> 
> On Thu, 11 Mar 2004, Peter Williams wrote:
> 
>>Richard B. Johnson wrote:
>>
>>>People who develop kernel code know the difference between
>>>'==' and '=' and are never confused my them.
>>
>>And you never make typing mistakes?  That's admirable or should I say 
>>incredible.
> 
> 
> The thing is, people tend to make fewer typing mistakes of that kind, than 
> just plain logic errors from not thinking right about something.
> 
> And while "0 == foo" may be logically the same thing as "foo == 0", the 
> fact is, the latter is what people are used to seeing. And by being used 
> to seeing it, they have an easier time thinking about it.
> 
> As a result, using the former just tends to increase peoples confusion by
> making code harder to read, which in turn tends to increase the chance of 
> bugs.
> 
> So don't do it. The kind of bug that the "0 == x" syntax protects against
> is LESS LIKELY to happen than the kind of bug it tends to cause.
> 
> 		Linus

OK.  I'll change all of such occurences in our EBS patches.

As somebody pointed out -Wall will (help) detect most of these errors by 
suggesting () be placed around any expression of the form a = b that 
occurs inside a simple boolean expression which will cause those people 
who care about eliminating warning messages to reevaluate the code and 
make sure they really meant a = b and replace it with (a = b) to get rid 
of the warning error.

The reason that I say "most" rather than "all" is (that testing shows) 
that if the a = b is part of a more complex expression and is already in 
() in order to (for instance) ensure the desired precedence -Wall will 
not flag it as a possible problem.

Peter
-- 
Dr Peter Williams, Chief Scientist                peterw@aurema.com
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