[poky] About the operator "??="

[Xu, Dongxiao]

Hi Richard,

Do you have comments on this one?

Thanks,
Dongxiao

Xu, Dongxiao wrote:
> Hi Richard,
> 
> Recently when investigating the file parsing speed, I found the
> implementation of "??=" is another hot spot. This operator will not
> apply the default assignment until the end of the parse, which is
> different from "?=". According to current poky, the users for "??="
> is mostly the scm revisions stored in poky-default-revisions.inc.    
> 
> Currently the final assignment logic for "??=" is added in
> finalize(), which costs about 20% parsing time. 
> 
> The differences between "??=" and "?=" are straight forward, however
> I don't fully understand in which senario the "??=" should be used.
> Or in other word, why those scm revisions should use "??=". Could you
> help to clarify a bit? Thanks so much!   
> 
> BTW, I noticed that openembedded doesn't use this operator.
> 
> Best Regards,
> -- Dongxiao