On 10/31/2014 05:55 PM, Gábor Csárdi wrote:
On Fri, Oct 31, 2014 at 8:16 PM, William Dunlap <wdun...@tibco.com> wrote:
You can put the following 3 objects, an environment and 2 functions
that access it, in any package that need some package-specific
storage (say your pkgB1 and pkgB2).
.pkgLocalStorage <- new.env(parent = emptyenv())
assignInPkgLocalStorage <- function(name, object) {
.pkgLocalStorage[[name]] <- object
}
getFromPkgLocalStorage <- function(name, object) {
.pkgLocalStorage[[name]]
}
Leave the environment private and export the functions. Then a user can
use them as
pkgB1::assignInPkgLocalStorage("myPallete", makeAPallete(1,2,3))
pkgB2::assignInPkgLocalStorage("myPallete", makeAPallete(5,6,7))
pkgB1::getFromPkgLocalStorage("myPallete") # get the 1,2,3 pallete
I am trying to avoid requiring pkgBn to do this kind of magic. I just
want it to call function(s) from pkgA. But maybe something like this
would work. In pkgBn:
my_palettes <- pkgA::palette_factory()
and my_palettes is a function or an environment that has the API
functions to modify my_palettes itself (via closure if it is a
function), e.g.
my_palettes$add_palette(...)
my_palettes$get_palette(...)
or if it is a function, then
my_palettes(add(...), ...)
my_palettes(get(...), ...)
etc.
This would work, right? I'll try it in a minute.
You'll need pkgA to be able to know that pkgB1's invokation is to use pkgB1's
parameters, so coupling state (parameters) with function, i.e., a class with
methods. So a solution is to use an S4 or reference class and generator to
encapsulate state and dispatch to appropriate functions, E.g.,
.Plotter <- setRefClass("Plotter",
fields=list(palette="character"),
methods=list(
update(palette) {
.self$palette <- palette
},
plot=function(...) {
graphics::plot(..., col=.self$palette)
}))
APlotter <- function(palette=c("red", "green", "blue"))
.Plotter(palette=palette)
PkgB1, 2 would then
plt = APlotter()
plt$plot(mpg ~ disp, mtcars)
plt$update(c("blue", "green"))
plt$plot(mpg ~ disp, mtcars)
or
.S4Plotter <- setClass("S4Plotter", representation(palette="character")
S4Plotter <- function(palette=c("red", "blue", "green"))
s4plot <- function(x, ...) graphics::plot(..., col=x@palette))
(make s4plot a generic with method for class S4Plotter to enforce type).
Seems like this interface could be generated automatically in .onLoad() of pkgA,
especially if adopting a naming convention of some sort.
Martin
Gabor
If only one of pkgB1 and pkgB2 is loaded you can leave off the pkgBn::.
A package writer can always leave off the pkgBn:: as well.
Bill Dunlap
TIBCO Software
wdunlap tibco.com
On Fri, Oct 31, 2014 at 4:34 PM, Gábor Csárdi <csardi.ga...@gmail.com> wrote:
Dear All,
I am trying to do the following, and could use some hints.
Suppose I have a package called pkgA. pkgA exposes an API that
includes setting some options, e.g. pkgA works with color palettes,
and the user of the package can define new palettes. pkgA provides an
API to manipulate these palettes, including defining them.
pkgA is intended to be used in other packages, e.g. in pkgB1 and
pkgB2. Now suppose pkgB1 and pkgB2 both set new palettes using pkgA.
They might set palettes with the same name, of course, they do not
know about each other.
My question is, is there a straightforward way to implement pkgA's
API, such that pkgB1 and pkgB2 do not interfere? In other words, if
pkgB1 and pkgB2 both define a palette 'foo', but they define it
differently, each should see her own version of it.
I guess this requires that I put something (a function?) in both
pkgB1's and pkgB2's package namespace. As I see it, this can only
happen when pkgA's API is called from pkgB1 (and pkgB2).
So at this time I could just walk up the call tree and put the palette
definition in the first environment that is not pkgA's. This looks
somewhat messy, and I am probably missing some caveats.
Is there a better way? I have a feeling that this is already supported
somehow, I just can't find out how.
Thanks, Best Regards,
Gabor
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