Stavros Macrakis wrote:
On Tue, Mar 31, 2009 at 12:41 PM, Martin Morgan <mtmor...@fhcrc.org
<mailto:mtmor...@fhcrc.org>> wrote:
I don't konw about preferred, but one method is
pkgVars <- local({
x <- NULL
list(getX=function() x, setX=function(value) x <<- value)
})
with use
> pkgVars$getX()
...
This introduces a different programming paradigm (a list of functions)
that might not be familiar for end-users and is not readily amenable
to documentation.
Why "not readily amenable to documentation"? If the user doesn't need
in the sense that ?pkgVars$getX would not do anything useful (I guess --
perhaps if there were an alias, I don't really know) and that R CMD
check would not detect inconsistencies between 'usage', code, and
documentation, for instance.
to understand the structure, he can consider the "$" as simply part of
but that would be additional syntax for the user to learn, which would
be counter-productive.
the function name. And I wouldn't name it pkgVars but pkg.
In general I would rather expose the interface than the object, which
lead me to my so-called 'better way'.
A probably better way is
pkgVars <- new.env(parent=emptyenv())
getX <- function() get("x", pkgVars, inherits=FALSE)
setX <- function(value) assign("x", value, envir=pkgVars)
I think a simpler, clearer way to make getX etc. globally visible is:
local({
x <- NULL
getX <<- function() x
setX <<- function(value) x <<- value
})
By 'globally' you mean in the package name space, I guess (this is
relying on a fairly nuanced understanding of what the 'top' environment
is during package building). For me the paradigm of <<- to the top
environment (or first getX found in the search path) opens the door to
doing dumb things like overwriting user variables. Maybe a risk you're
willing to engage within your own name space...
Martin
To my taste, this is much cleaner than explicitly referencing environments.
-s
--
Martin Morgan
Computational Biology / Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N.
PO Box 19024 Seattle, WA 98109
Location: Arnold Building M2 B169
Phone: (206) 667-2793
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