On Tue, 5 Sep 2006, Thomas Lumley wrote:
>
> The partial matching is fairly deeply built in to complex assignment,
<sip>
> because as evalseq works through the nested calls on the LHS the code
> being called doesn't know it is in an assignment call.
The problem in
> D = list(ABCD=2:1)
> D$ABC[]<-3:4
> D
$ABCD
[1] 3 4
$ABC
[1] 3 4
is that eval.c:evalseq ends up with a reference to D$ABCD from evaluating
D$ABC with partial matching. Since evalseq doesn't (and shouldn't)
increase NAMED on these partially evaluated calls, NAMED is still 1 for
D$ABCD. When evalseq's D$ABC has 3:4 assigned into it the vector is
changed directly, since NAMED=1, and both D$ABC and D$ABCD change.
The minimal fix would appear to be the horrible hack of incrementing NAMED
whenever a list element is even looked at with partial matching. Otherwise
evalseq would have to be taught to recognize aliasing from partial
matching.
-thomas
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