setDT not always sets ".internal.selfref"

Reading #6862 I found this behaviour:

ds = copy(datasets::iris)
x = setDT(get("ds"))
attr(ds, ".internal.selfref")   # <pointer...>

ds = copy(datasets::iris)
x = setDT(get0("ds"))            # note get0
attr(ds, ".internal.selfref")    # NULL

Both ds's set as data.table's but in the second form, ds lacks selfref.
AFAIK setalloccol() is shallow copying ds, but then setDT fails to reassign it to the symbol ds because not recognizing 'get0' bindimg.
Arguably there is no easy way to detect the binding for every possible call that returns a data.table bound to a symbol, so I think setDT should warn when it is unable to assign it back -if a shallow copy is made-. or if ds lacks selfref before returning.
However, x does have it, and thus identical(ds, x) fails in second case.
Related perhaps #6754

I think in this case we can continue the kludge pretty easily -- there's already logic for get(), it was just written before get0() existed (? or at least was more well-known):

data.table/R/data.table.R

Line 2990 in 3afc750

} else if (name %iscall% "get") { # #6725

Note also #6702

@MichaelChirico

Hi @MichaelChirico @rikivillalba

Can I work on this issue .
As suggested by Michael, I'll update the existing logic in setDT() to handle get0() similarly to get():

else if (name %iscall% c("get", "get0"))

Is this approach working good or is there anything else you would like to suggest?
Thanks!

Let's get #6802 finished first, since it is likely to generate conflict with that change

@MichaelChirico

hi @MichaelChirico now as the issue #6702 is finished can i work on this issue
i have proposed solution for it.
thanks for your time

(textproc/R-data.table) Updated 1.16.4 to 1.18.4, Fix build against 4…

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setDT not always sets ".internal.selfref" #6864

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setDT not always sets ".internal.selfref" #6864

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MichaelChirico commented on Mar 12, 2025

venom1204 commented on Mar 13, 2025

MichaelChirico commented on Mar 14, 2025

venom1204 commented on Jun 24, 2025

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