cubranic at stat.ubc.ca
Fri Apr 1 04:49:43 CEST 2011
On 31 March 2011 at 3:53 PM, Sean Robert McGuffee wrote:
> This link has a lot of information in it, but I don't understand much
> of it because it seems to be written for people who already
> understand it.
You make a very good point here, and I think it's largely true for most
of R's documentation. But that's because it's a reference, not a
tutorial, and succinctness is valued more than hand-holding. That's what
man pages are, too, btw.
I actually think R-exts should be even more like a reference, or (more
likely) it should have a reference-like counterpart. Like you showed
with "useDynLib", important functions are described conversationally,
instead of formally and exhaustively, they way help pages do for user-
> Under section 1.6: For example, I'm having trouble figuring out the
> meaning of the following terms and or phrases:
> name spaces, management system, package writer, top level package
> directory, name space directives, imports, exports
I don't mean to be glib, but how do you expect to get anywhere with
packages when you don't understand basic concepts behind modularity like
exporting a function so it's callable outside a module? As a first
resort, look it up on Wikipedia: the article on name spaces ought to
clear up a few things at least.
A good way to avoid frustration is to read the manual lazily, start your
code small and build up. For instance, you probably don't know what the
section 1.6.2 on S3 methods is going on about because you're not using
S3 classes in your code. if that's the case, fine, you don't need to read
how to deal with them in the package declarations.
I grant you that some terms are needlessly obfuscated, though. For
example, "package writer" could have been "package author" -- but,
honestly, is that really that hard to figure out?
> "There can be one or more useDynLib directives which allows shared
> objects that need to be loaded to be specified in the NAMESPACE
> file. The directive
> This also is followed by other inconsistent examples:
> "useDynLib(foo, myRoutine, myOtherRoutine)"
> "myDLL = useDynLib(foo, myRoutine_sym = myRoutine, myOtherRoutine)"
I'm sorry, but after re-reading this section, i don't see any
inconsistency. There are different ways of calling "useDynLib", but what
they do is explained in the text. And, back to reading the manual
lazily, only the first one is used in 99% of the time. I, for one, use
Rcpp extensively, and never needed (or even known) anything other than
the very first one form of useDynLib. (And, in all likelihood, might have
just used whatever Rcpp.package.skeleton put into the NAMESPACE for me.)
> Does anyone have any links to something more like an API of what
> appears to be some type of function called useDynLib?
> In particular, I'm looking to find out what arguments the method
> useDynLib takes with descriptions of their types?
I don't know of one, but can you describe what exactly you're trying to
do? If all you need is allow the R code in your package to call into a
dynamic library "mylib.so" that's distributed with the package, it is
sufficient to have a declaration "useDynLib(mylib)". This will ensure that
when the package is loaded into the session, the dynamic library will
also be loaded and ready for calling into with ".Call" and related
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