[Rd] for in r-devel

[Gabor Grothendieck]

Regarding, this news item for r-devel:

‘for()’ loops are generalized to iterate over any object with ‘[[’ and
‘length()’ methods. Thanks to Hervé Pagès for the idea and the patch.

Below dd is an object for which [[ and length work but the result is
still numeric rather than Date class in  "R Under development
(unstable) (2016-03-15 r70334)" as observed in the comments to:
http://stackoverflow.com/questions/36074344/why-does-for-convert-date-to-numeric#comment59794873_36074344
Expanding on that:

    dd <- Sys.Date() + 0:1

    dd[[1]]  # [[ works
    ## [1] "2016-03-18"

    length(dd)  # length works
    ## [1]  2

    for(d in dd) str(d)  # gives numeric rather than Date class
    ## num 16878
    ## num 16879


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