[Python-Dev] cpython: fix compiler warning by implementing this more cleverly

[Terry Reedy]

On 11/22/2011 7:42 PM, Benjamin Peterson wrote:
> 2011/11/22 Antoine Pitrou<solipsis at pitrou.net>:
>> On Tue, 22 Nov 2011 16:42:35 -0500
>> Benjamin Peterson<benjamin at python.org>  wrote:
>>> 2011/11/22 Antoine Pitrou<solipsis at pitrou.net>:
>>>> On Tue, 22 Nov 2011 21:29:43 +0100
>>>> benjamin.peterson<python-checkins at python.org>  wrote:
>>>>> http://hg.python.org/cpython/rev/77ab830930ae
>>>>> changeset:   73697:77ab830930ae
>>>>> user:        Benjamin Peterson<benjamin at python.org>
>>>>> date:        Tue Nov 22 15:29:32 2011 -0500
>>>>> summary:
>>>>>    fix compiler warning by implementing this more cleverly
>>>>
>>>> You mean "more obscurely"?
>>>> Obfuscating the original intent in order to disable a compiler warning
>>>> doesn't seem very wise to me.
>>>
>>> Well, I think it makes sense that the kind tells you how many bytes are in it.
>>
>> Yes, but "kind * 2 + 2" looks like a magical formula, while the
>> explicit switch let you check mentally that each estimate was indeed
>> correct.
>
> I don't see how it's more magic than hardcoding 4, 6, and 10. Don't
> you have to mentally check that those are correct?

I personally strongly prefer the one-line formula to the hardcoded magic 
numbers calculated from the formula. I find it much more readable. To 
me, the only justification for the switch would be if there is a serious 
worry about the kind being changed to something other than 1, 2, or 4. 
But the fact that this is checked with an assert that can be optimized 
away negates that. The one-liner could be followed by
   assert(kind==1 || kind==2 || kind==4)
which would also serve to remind the reader of the possibilities. You 
could even follow the formula with /* 4, 6, or 10 */ I think you 
reverted too soon.

-- 
Terry Jan Reedy