Top-level code in packages
On Fri, 2 Jul 2004, Frank E Harrell Jr wrote:
Brian Ripley stated that in the future it will not be a good idea to have top-level code in R packages other than assignments. There is one important exception, though it leads instantly to an assignment. To maintain compatibility across multiple platforms (R, S-Plus, and more than one version of each, Windows, Linux, etc.) I frequently use if( ) statements to conditionally define functions depending on the operating system and the version of R or S-Plus in effect.
That _is_ a top-level assignment. `Defining' a function is actually
assigning a value to a symbol, and code inside if, for, etc is executed at
top level.
I prefer to write
foo <- if(tools:::.OStype() == "windows") {...} else {...}
for conditional `definitions' precisely because it is clearer that is what
is going on.
BTW, if you want to test the OS you can't do it with .Platform$OS.type and
allow cross-building, hence the test illustrated.
Brian D. Ripley, ripley@stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595