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\note{
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\note{
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  Functions \code{oldClass} and \code{oldClass<-} behave in the same way
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  Functions \code{oldClass} and \code{oldClass<-} behave in the same way
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  as functions of those names in S-PLUS 5/6, \emph{but} in \R
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  as functions of those names in S-PLUS 5/6, \emph{but} in \R
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  \code{\link{UseMethod}} dispatches on the class as returned by
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  \code{\link{UseMethod}} dispatches on the class as returned by
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  \code{class} rather than \code{oldClass}.
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  \code{class} rather than \code{oldClass}.  \emph{However},
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  \link{group generic}s dispatch on the \code{oldClass} for efficiency.
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}
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}
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\section{Formal classes}{
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\section{Formal classes}{
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  An additional mechanism of \emph{formal} classes has been available in
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  An additional mechanism of \emph{formal} classes is available in
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  packages \pkg{methods} since \R 1.4.0, and as from \R 1.7.0 this
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  packages \pkg{methods} which is attached by default.  For objects
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  is attached by default.  For objects which have a formal class, its name
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  which have a formal class, its name is returned by \code{class}
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  is returned by \code{class} as a character vector of length one.
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  as a character vector of length one.
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  The replacement version of the function sets the class to the value
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  The replacement version of the function sets the class to the value
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  provided.  For classes that have a formal definition, directly
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  provided.  For classes that have a formal definition, directly
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  replacing the class this way is strongly deprecated.  The expression
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  replacing the class this way is strongly deprecated.  The expression
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  \code{\link[methods]{as}(object, value)} is the way to coerce an object to a
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  \code{\link[methods]{as}(object, value)} is the way to coerce an object to a
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  particular class.
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  particular class.
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}
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}
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\seealso{
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\seealso{
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  \code{\link{UseMethod}}, \code{\link{NextMethod}}.
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  \code{\link{UseMethod}}, \code{\link{NextMethod}},
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  \code{\link{group generic}}.
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}
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}
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\examples{
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\examples{
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  x <- 10
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x <- 10
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  inherits(x, "a") #FALSE
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inherits(x, "a") #FALSE
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  class(x)<-c("a", "b")
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class(x) <- c("a", "b")
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  inherits(x,"a") #TRUE
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inherits(x,"a") #TRUE
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  inherits(x, "a", TRUE) # 1
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inherits(x, "a", TRUE) # 1
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  inherits(x, c("a", "b", "c"), TRUE) # 1 2 0
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inherits(x, c("a", "b", "c"), TRUE) # 1 2 0
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}
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}
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\keyword{methods}
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\keyword{methods}
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\keyword{classes}
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\keyword{classes}