On 2024-12-04 1:25 p.m., Adelchi Azzalini wrote:
Hi. I am working on the development of an existing package (smof, on CRAN). My
current aim is widen the list of possible optimizers from which the user can
select one method for optimizing a certain task. Well-known possibilities
within the base package are optim (with various options) and nlminb. Besides
these, I am thinking of including also those of package nloptr, but without
forcing users to install this package which perhaps they don't need for other
purposes. Hence, I would like to import nloptr only if it is available on the
user system; it not, I can just confine the list of optimizers to optim and
nlminb.
This idea implies a sort of “conditional import” of nloptr. Is this possible? Section
1.1.3.1 "Suggested packages" of
https://translation.r-project.org/man/R-exts/R-exts-ko.html#Suggested-packages
seems to hint at such a possibility. See the use of requireNamespace in the
second paragraph.
After elaborating along this line, I packaged my code, with nloptr listed on
the line Suggests of DESCRIPTION. However this attempt failed a the “R CMD
check “ stage with message
Namespace dependency missing from DESCRIPTION Imports/Depends entries: ‘nloptr’
In addition, I have no idea of how to declare a "conditional import” in
NAMESPACE.
Is this idea of “conditional import” totally unfeasible, then?
The usual way to do this is to list the package in Suggests, and then
wrap any use of it in `if (requireNamespace("pkg")) { ... }` blocks.
This doesn't quite import the functions, you would need to use the
`pkg::fn` syntax to access the functions.
If you really want to simulate importing so that you don't need the
`pkg::` prefix, you could do it this way: In the `.onLoad` function of
your package, you would have code like
if (requireNamespace("pkg")) {
foo <- pkg::foo
bar <- pkg::bar
} else {
foo <- stub
bar <- stub
}
where `stub` is a function that says "you need `pkg` to use this function".
Duncan Murdoch
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