hi all -- i looked through the R Language Definition document, but couldn't
find any particular warning or example that would clarify the best use of
attribute setting for R objects.

let x be some R object, and i'd like to add attribute "foo" with value
"bar".

case 1:
> attr(x, "foo") <- "bar"

case 2:
> attributes(x)$foo <- "bar"

in both cases, attributes(x) reveals the appropriate setting has taken
place.
i'm assuming that attr(...) is 'safer' in the sense that perhaps
consistency checks are made?
(almost like a generic accessor/setter method?)
but i also haven't seen any examples where case 2 (above) would bad... is
there are trivial such example out there?

BTW -- the cause for interest here is when dealing with dendrogram objects,
for which much of the useful data are stored as attributes, and where
running dendrapply means having to explicitly set attribute values to
retain the tree structure in the resulting object.

cheers,

-m

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