On 07/10/2013 10:29 AM, Rainer M Krug wrote:
Hi
First, sorry if I get the terminology wrong, I am still quite new to the
concept of using environments and workspaces.
Say I have a statement in a package SIM like
sim <- TYPE
where the variable TYPE is initialized in the package to
e.g. "exponential" (SIM::TYPE == "exponential").
Now, I want to give the user the option of specifying the variable TYPE,
but to the effect, that if the user does not define a variable TYPE in
the user workspace (.GobalEnv), the one in the namespace from the
package is used.
In other words, I want to look first in the workspace, and then in SIM::
for the variable TYPE. How can do this?
The rgl package does this when looking for defaults for graphics. Here's
the code:
getr3dDefaults <- function()
tryCatch(get("r3dDefaults", envir=.GlobalEnv),
error = function(e) r3dDefaults)
This will find the variable r3dDefaults if it is in the global
environment or in a package on the search path; if that fails, it
returns the local one. Since that function is defined in the package,
it can see the local r3dDefaults variable. You might not want to accept
anything except what is in .GlobalEnv; in that case, use inherits =
FALSE in the call to get().
Duncan Murdoch
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