Kasper Daniel Hansen wrote:
I am considering a package with a namespace (Rgraphviz from Bioc). I
essentially want to have some error handling for loading the dll,
something like wrapping it into tryCatch or similar (reason: see below).
Right now I am loading the dynamic libraries by useDynLib in my
NAMESPACE file. When I look at the code from loadNamespace, I have the
impression that what I want is impossible (.onLoad and the user settable
hooks are called after the dynamic libraries have been loaded). Is that
true? And is the only way to proceed, to not use useDynLib in my
NAMESPACE file, but instead load the dynamic libraries manually in .onLoad?
Reason for my wish: on Windows Rgraphviz links to Graphviz which the
user needs to install themselves. Unfortunately there are many versions
of Graphviz and they tend to be incompatible with each other, to the
extent that certain libraries have been renamed. This has been causing a
lot of confusion since the Windows binaries have been compiled with one
specific version, and sometimes the loading of the dll itself fails
because the libraries have been renamed.... I am attempting to inject
some kind of helpful error message along the lines of "it looks like you
did not have version XXX of Graphviz installed". For that to happen, I
need to do a tryCatch. There is a potential similar problem for binaries
on OS X (but somewhat fewer complaints).
At first, I do not answer your question, but make your request more
complicated:
It is even hard to find "version XXX of Graphviz", because the numbers
in the names of the distributed graphviz zip files and the actual
versions of graphviz are also not always the same. Beside that the
graphviz folks obviously even change API specifications in patch-level
releases.
Then to your question: I think your are right and need it in .onLoad
where you can finally check if the dll has been loaded and generate erro
messages.
Good luck,
Uwe
I could see the use for this for other packages that depends on external
DLLs.
Thanks
Kasper
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