>
>
>> However, modifying a list contained in an environment *does* result in
>> a copy -- tracemem prints out some info when we do the assignment:
>> e <- new.env(parent = emptyenv())
>> e$x <- list(1)
>> tracemem(e$x)
>> # [1] "<0x1148c1708>"
>> e$x[[1]] <- 2
>> # tracemem[0x1148c1708 -> 0x11b2fc1b8]:
>>
>
> Currently e$x marks values as immutable if they have any references by
> setting NAMED to 2. You can see this with
>
> e <- new.env(parent = emptyenv())
>> e$x <- list(1)
>> .Internal(inspect(e))
>>
> @30b2498 04 ENVSXP g0c0 [NAM(1)] <0x30b2498>
> ENCLOS:
> @2600e98 04 ENVSXP g0c0 [MARK,NAM(2)] <R_EmptyEnv>
> HASHTAB:
> @2e41540 19 VECSXP g0c7 [] (len=29, tl=1)
> @25c9628 00 NILSXP g0c0 [MARK,NAM(2)]
> @25c9628 00 NILSXP g0c0 [MARK,NAM(2)]
> @25c9628 00 NILSXP g0c0 [MARK,NAM(2)]
> @25c9628 00 NILSXP g0c0 [MARK,NAM(2)]
> @30b3370 02 LISTSXP g0c0 []
> TAG: @2637870 01 SYMSXP g0c0 [MARK,NAM(2)] "x"
> @3569488 19 VECSXP g0c1 [NAM(1)] (len=1, tl=0) ## <--- NAM = 1
> @35694e8 14 REALSXP g0c1 [NAM(2)] (len=1, tl=0) 1
> ...
>
>> e$x
>>
> [[1]]
> [1] 1
>
> .Internal(inspect(e))
>>
> @30b2498 04 ENVSXP g0c0 [NAM(1)] <0x30b2498>
> ENCLOS:
> @2600e98 04 ENVSXP g0c0 [MARK,NAM(2)] <R_EmptyEnv>
> HASHTAB:
> @2e41540 19 VECSXP g0c7 [] (len=29, tl=1)
> @25c9628 00 NILSXP g0c0 [MARK,NAM(2)]
> @25c9628 00 NILSXP g0c0 [MARK,NAM(2)]
> @25c9628 00 NILSXP g0c0 [MARK,NAM(2)]
> @25c9628 00 NILSXP g0c0 [MARK,NAM(2)]
> @30b3370 02 LISTSXP g0c0 []
> TAG: @2637870 01 SYMSXP g0c0 [MARK,NAM(2)] "x"
> @3569488 19 VECSXP g0c1 [NAM(2)] (len=1, tl=0) ## <--- NAM = 2
> @35694e8 14 REALSXP g0c1 [NAM(2)] (len=1, tl=0) 1
> ...
>
> It is not clear if this is needed or just done in an abundance of
> caution. If R is built to use reference counting for determining
> sharing information this does not happen, so this is likely to change
> and not force a copy by 3.4.0.
>
Excellent, that's great to hear!
-Winston
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