I agree with almost everything Deepayan said, but would add one thing:
On 21/10/2021 3:41 a.m., Deepayan Sarkar wrote:
...
My suggestion is having a package-specific environment, and Duncan's
is to have a function-specific environment. If you only need this for
this one function, then that should be good enough. If you eventually
want to access the persistent information from multiple functions,
having a package-specific environment would be more useful.
I agree with that statement, but those aren't the only two choices.
Your local() call can create several functions and return them in a
list; then just those functions have access to the local variables. For
example,
createFns <- local({
.fooInfo <- NULL
fn1 <- function (...) { ... }
fn2 <- function (...) { ... }
list(fn1 = fn1, fn2 = fn2)
})
fns <- createFns()
fn1 <- fns$fn1
fn2 <- fns$fn2
Now fn1 and fn2 are functions that can see .fooInfo, and nobody else can
(without going through contortions).
One other difference between this approach and the package-specific
environment: there's only one package-specific environment in
Deepayan's formulation, but I could call createFns() several times,
creating several pairs of functions, each pair with its own independent
version of .fooInfo.
I don't know if that's something that would be useful to you, but
conceivably you'd want to maintain partial plots in several different
windows, and that would allow you to do so.
And there are other choices too: there are several packages
implementing object systems that allow objects to maintain persistent
data. I haven't used those, so this list may contain omissions and
errors: R6, R.oo, proto.
Duncan Murdoch
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