I am trying to follow directions at
http://cran.r-project.org/doc/manuals/r-patched/R-exts.html#Suggested-packages
regarding handling suggested packages with requireNamespace() rather
than require(), and I have some questions.
1/ When I do requireNamespace() in a function is the loading of the
namespace only effective within the function?
2/ At the link above in the manual it says "Note the use of rgl:: as
that object would not necessarily be visible...". When the required
package is loading methods, will the method be found when I reference
the generic, which is not in the package, or do I need to do something
different?
3/ In some packages I have functions that return an object defined in
the suggested package being required. For example, a function does
require("zoo") and then returns a zoo object. So, to work with the
returned object I am really expecting that zoo will be available in the
session afterwards. Is it recommended that I just check if the package
is available on the search path the user has set rather than use
require() or requireNamespace()?.
Regarding checking the path without actually attaching the package to
the search path, is there something better than "package:zoo" %in%
search() or is that the best way?
4/ I have a function in a package that Depends on DBI and suggests
RMySQL, RPostgreSQL, RSQLite. The function uses dbDriver() in DBI which
uses do.call(). If I use requireNamespace() in place of require() I get
> requireNamespace("RMySQL")
Loading required namespace: RMySQL
> m <- dbDriver("MySQL")
Error in do.call(as.character(drvName), list(...)) :
could not find function "MySQL"
> require("RMySQL")
Loading required package: RMySQL
> m <- dbDriver("MySQL")
>
Is there a different way to handle this without altering the search path?
The function do.call() does not seem to work with an argument like
do.call("RMySQL::MySQL", list())
even at the top level, and this situation may be more complicated when
it is in a required package. What am I missing?
Thanks,
Paul
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