On Sunday, January 28, 2024 5:36 PM, Paul Smith wrote: >On Sat, 2024-01-27 at 17:45 -0500, rsbec...@nexbridge.com wrote: >> My take on it is that +:= (because of the : ) means that you have to >> resolve everything at that point. > >Yes, I understand what you are saying. The question is, is that the right >conception? >Here's another way to look at it: > > FOO +:= bar > >can be interpreted as working like this: > > FOO := $(FOO) bar > >which is what you and others are arguing for. Or it can be interpreted as >working >like this: > > __FOO := bar > FOO += $(__FOO) > >(where the value of __FOO is immutable). This is what I was thinking.
I do not think the above two are equivalent. FOO += $(__FOO) will not be immutable until it is referenced. __FOO is immutable on the basis of the :=, but += is a lazy instantiation, by definition. Changing that semantic would have fairly broad impacts. >My argument is, if you want to write "FOO := $(FOO) bar" you can just write >that >today: you don't need "+:=" (you will have an extra leading space if FOO was >not set >already but that's unlikely to matter much). > >But if you want the second form it's tricky to do. > >It can also be argued that the second form is closer to the behavior of "+=" >since >"+=" keeps the pre-existing type of the variable rather than changing it. >Although of >course it's still special in some respects.
