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).
I could see the use for this for other packages that depends on
external DLLs.
Thanks
Kasper
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