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A general description is here.
‘serialize()’ and ‘unserialize()’ are no longer described as ‘experimental’. The interface is now regarded as stable, although the serialization format may well change in future releases. (‘serialize()’ has a new argument ‘version’ which would allow the current format to be written if that happens.)
New functions ‘saveRDS()’ and ‘readRDS()’ are public versions of the ‘internal’ functions ‘.saveRDS()’ and ‘.readRDS()’ made available for general use. The dot-name versions remain available as several package authors have made use of them, despite the documentation. ‘readRDS()’ no longer wraps non-file connections in a call to ‘gzcon()’, for efficiency (see its documentation).
‘saveRDS()’ supports ‘compress = "xz"’.