RE: New conditional assignm ent facility

[rsbecker]

On Saturday, January 27, 2024 3:33 PM, Paul Smith wrote:
>On Mon, 2024-01-22 at 08:15 -0500, Paul Smith wrote:
>> Let's step back and I'll try to think more clearly about this.
>
>Sorry for the delay in replying.
>
>I can see that I was thinking about this one way but there's another way to 
>look at it
>that I didn't think of.  We are talking only about
>(a) append operators _other than_ +=, and (b) situations where the variable 
>already
>has a value when the append operator is parsed.
>
>In all cases we would expand the right-hand side of the variable according to 
>the
>assignment operator: e.g., if it were +:= we would immediately expand the RHS.
>
>My proposal was to keep the type of variable (recursive vs. simple) the same 
>and
>then "fix up" the result of the RHS so it could be appended in a correct way.  
>In this
>conception the operator applies ONLY to the RHS value, and will set the type 
>of the
>variable only if the variable doesn't already exist, as a side-effect.
>
>The other way to think about it is that the assignment operator overrides the 
>type
>of the variable as well: we would re-evaluate the LHS value then append the 
>RHS.
>E.g., if it were +:= we would immediately expand the RHS as well and change the
>type of simple.  In this conception the operator resets the type of the 
>variable as its
>primary function, not just as a side-effect, and modifies not just the RHS 
>value but
>also (possibly) the LHS value as well.
>
>An example to make this clearer:
>
>Given:
>
>    foo = 1
>      bar   = $(foo)
>    foo = 2
>      bar +:= $(foo)
>    foo = 3
>      bar  += $(foo)
>
>    $(info bar=$(bar))
>
>In my original version, the result would be that "bar" is a recursive variable 
>with the
>value "$(foo) 2 $(foo)" and the output of the info function would be "bar=3 2 
>3".
>
>In the alternative version, the result would be that "bar" is a simple 
>variable with the
>value "2 2 3" and the output of the info function would obviously be "bar=2 2 
>3".
>
>I'm interested in peoples' opinions about which of these two implementations 
>they
>would feel to be more "intuitive" or "correct".
>Also please consider issues of "action at a distance" where a variable is 
>assigned in
>one makefile and appended to in some other makefile, potentially far away.
>
>
>This discussion has really helped me crystallize the differences and should 
>make the
>resulting documentation, if/when it's written, much more clear so I definitely
>appreciate it!

Intuitive reading of this would seem that "bar=2 2 3" is better, as +:= should 
force complete resolution of the string applied to bar, not partial resolution 
of foo keeping an instance of $(foo) for resolution later.

Just my $0.02.
Randall