30update.txt

Updating packages for 3.0.0
===========================

Package maintainers should be aware of the following changes scheduled
to appear in 3.0.0 on March/April 2013.


Namespaces
==========

Packages must have namespaces (as they have since R 2.14.0), but a
default NAMESPACE file is no longer generated on installation (it
still is by R CMD build).  .First.lib is no longer run, so start-up
code must be in either .onLoad or .onAttach.

The one exception is data-only packages without any R code: but even
for those it is better to add an empty NAMESPACE file.


Long vectors
============

On 64-bit platforms, the length of a vector is no longer limited to
2^31-1 elements.  This applies to matrices and arrays, but for the
forseeable future each of their dimensions is limited to 2^31-1.

The most important consequence is that length(x) is now more likely to
not be an integer.  (This has always been a possibility for length()
methods, and e.g. package Matrix had methods that return a double.)
Programmers have frequently assumed that lengths were integers when
passing to .C/.Fortran, and furthermore that as.integer(length(x)) was
not NA.  So safe code will

- always use as.integer(length(x)) when calling .C/.Fortran
- if using NAOK = TRUE, check that the result is not NA.

As a precaution, .C and .Fortran do not accept long vectors (as a
common idiom is to pass a vector and its length).