[Rd] Repeated library() of one package with different include.only= entries

[Martin Maechler]

>>>>> Michael Chirico 
>>>>>     on Mon, 8 Apr 2024 10:19:29 -0700 writes:

    > Right now, attaching the same package with different include.only= has no
    > effect:

    > library(Matrix, include.only="fac2sparse")
    > library(Matrix)
    > ls("package:Matrix")
    > # [1] "fac2sparse"

    > ?library does not cover this case -- what is covered is the _loading_
    > behavior of repeated calls:

    >> [library and require] check and update the list of currently attached
    > packages and do not reload a namespace which is already loaded

    > But here we're looking at the _attach_ behavior of repeated calls.

    > I am particularly interested in allowing the exports of a package to be
    > built up gradually:

    > library(Matrix, include.only="fac2sparse")
    > library(Matrix, include.only="isDiagonal") # want: ls("package:Matrix") -->
    > c("fac2sparse", "isDiagonal")
    > ...

    > It seems quite hard to accomplish this at the moment. Is the behavior to
    > ignore new inclusions intentional? Could there be an argument to get
    > different behavior?

As you did not get an answer yet, ..., some remarks by an
R-corer who has tweaked library() behavior in the past :

- The `include.only = *` argument to library() has been a
  *relatively* recent addition {given the 25+ years of R history}:

  It was part of the extensive new features by Luke Tierney for
  R 3.6.0  [r76248 | luke | 2019-03-18 17:29:35 +0100], with NEWS entry

    • library() and require() now allow more control over handling
      search path conflicts when packages are attached. The policy is
      controlled by the new conflicts.policy option.

- I haven't seen these (then) new features been used much, unfortunately,
  also not from R-core members, but I'd be happy to be told a different story.
  

For the above reasons, it could well be that the current
implementation {of these features} has not been exercised a lot
yet, and limitations as you found them haven't been noticed yet,
or at least not noticed on the public R mailing lists, nor
otherwise by R-core (?).

Your implicitly proposed new feature (or even *changed*
default behavior) seems to make sense to me -- but as alluded
to, above, I haven't been a conscious user of any
'library(.., include.only = *)' till now.

Martin

--
Martin Maechler
ETH Zurich   and  R Core