Salut,
I have a question regarding the usage of the weak default value operator ??=
I do understand the rules associated with this operator, in particular wrt. to
the other assignment operators = and ?=
Could someone shed some lights on why "??=" was introduced in the first place?
I couldn't find the relevant thread on the yocto MLs :(
Modulo my little understanding of Yocto, I have worked out a scenario where
"??=" would make sense... But not sure if a) this understanding is correct, and
b) if it was indeed (one of) the motivation for "??=". I prefer getting "first
(developer) hand info" whenever possible :)
possible explanation for "??=":
AFAIK, bitbake will parse configuration files in a certain order, starting from
bblayers.conf, then going to the corresponding layer.conf, then bitbake.conf,
then the conf/{site,auto,local}.conf etc. If a default value for -- say FOO --
is set using the ?= operator in one of the config file parsed before by
bitbake, then there is no way to redefine/customize that default value later on
(by the way ?= works). We could set it (using standard = operator), but that
might be too strong (for the cases where we want to have another default value
if not set). This is where the ??= operator could be very handy.
Am I on the right track or is it just a nice story? Any pointers (ML thread,
source code, explanation) about the motivation behind "??=" operator is greatly
appreciated. TIA!
Cheers!
ljd, 0x5f375a86
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