[Rd] How do I reliably and efficiently hash a function?

[Konrad Rudolph]

Thanks. I know about `local` (and functions within functions). In
fact, the functions are *already* defined inside their own environment
(same as what `local` does). But unfortunately this doesn’t solve my
problem, since the functions’ parent environment gets changed during
the function’s execution, and I need to retrieve my stored data
*after* that point, inside the function.

I’ve tried to create a more exact example of what’s going on —
unfortunately it’s really hard to simplify the problem without losing
crucial details. Since the code is just a tad too long, I’ve posted it
as a Github Gist:

https://gist.github.com/klmr/53c9400e832d7fd9ea5c

The function `f` in the example calls `get_meta()` twice, and gets
different results before and after calling an ancillary function that
modifies the function’s `parent.env`. I want it to return the same
information (“original”) both times.

On Fri, Dec 11, 2015 at 10:49 AM, Mark van der Loo
<mark.vanderloo at gmail.com> wrote:
> In addition to what Charles wrote, you can also use 'local' if you don't
> want a function that creates another function.
>
>> f <- local({info <- 10; function(x) x + info})
>> f(3)
> [1] 13
>
> best,
> Mark
>
>
> Op vr 11 dec. 2015 om 03:27 schreef Charles C. Berry <ccberry at ucsd.edu>:
>>
>> On Thu, 10 Dec 2015, Konrad Rudolph wrote:
>>
>> > I’ve got the following scenario: I need to store information about an
>> > R function, and retrieve it at a later point. In other programming
>> > languages I’d implement this using a dictionary with the functions as
>> > keys. In R, I’d usually use `attr(f, 'some-name')`. However, for my
>> > purposes I do not want to use `attr` because the information that I
>> > want to store is an implementation detail that should be hidden from
>> > the user of the function (and, just as importantly, it shouldn’t
>> > clutter the display when the function is printed on the console).
>> >
>> > `comment` would be almost perfect since it’s hidden from the output
>> > when printing a function — unfortunately, the information I’m storing
>> > is not a character string (it’s in fact an environment), so I cannot
>> > use `comment`.
>> >
>> > How can this be achieved?
>> >
>>
>> See
>>
>> https://cran.r-project.org/doc/manuals/r-release/R-intro.html#Scope
>>
>> For example, these commands:
>>
>> foo <- function() {info <- "abc";function(x) x+1}
>> func <- foo()
>> find("func")
>> func(1)
>> ls(envir=environment(func))
>> get("info",environment(func))
>> func
>>
>> Yield these printed results:
>>
>> : [1] ".GlobalEnv"
>> : [1] 2
>> : [1] "info"
>> : [1] "abc"
>> : function (x)
>> : x + 1
>> : <environment: 0x7fbd5c86bc60>
>>
>> The environment of the function gets printed, but 'info' and other
>> objects that might exist in that environment do not get printed unless
>> you explicitly call for them.
>>
>> HTH,
>>
>> Chuck
>>
>> p.s. 'environment(func)$info' also works.
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