reasonable to have methods that do not use the

package.  The generic is currently re-exported from the

namespace to allow packages importing it from

there to continue working, but this may change in future.

re-installed and package code using such generics from other

packages needs to ensure that they are imported rather than rely

on their being looked for on the search path (as in a namespace,

the base namespace has precedence over the search path).

Reference counting is now used instead of the

mechanism for determining when objects can be safely mutated in

base C code.  This reduces the need for copying in some cases and

should allow further optimizations in the future.  It should

help make the internal code easier to maintain.

This change is expected to have almost no impact on packages

using supported coding practices in their C/C++ code.

Perl-like regular expressions, if available.  (On non-Windows

platforms PCRE1 can optionally be used if PCRE2 is not available

at build time.)  The version of PCRE in use can be obtained

) has versions <= 8, PCRE2 versions >= 10.

strongly recommended (preferably version 10.30 or later) as PCRE1

PCRE2 reports errors for some regular expressions that were

accepted by PCRE1.  A hyphen now has to be escaped in a character

class to be interpreted as a literal (unless first or last in the

longer allowed in character classes (PCRE1 treated these as

(which is not back compatible with previous use of an unnamed second

, the utility for the data frame method of

, now works without parsing and explicit evaluation,

starting from Suharto Anggono's suggestion in

defaulting to true.  If set to false, missing

values now propagate into the interpolated values.

The internal traceback object produced when an error is

non-UTF-8 locale the output is marked as UTF-8.

Most functions with file-path inputs will give an explicit

error if a file-path input in a marked encoding cannot be

translated (to the native encoding or in some cases on Windows to

UTF-8), rather than translate to a different file path using