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\alias{function-class}
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\alias{function-class}
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\alias{ANY-class}
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\alias{ANY-class}
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\alias{VIRTUAL-class}
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\alias{VIRTUAL-class}
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\alias{missing-class}
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\alias{missing-class}
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\alias{S4-class}
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\alias{S4-class}
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\alias{namedList-class}
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\title{Classes Corresponding to Basic Data Types }
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\title{Classes Corresponding to Basic Data Types }
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\description{
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\description{
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  Formal classes exist corresponding to the basic R object types, allowing
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  Formal classes exist corresponding to the basic R object types, allowing
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  these types to be used in method signatures, as slots in class
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  these types to be used in method signatures, as slots in class
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  definitions, and to be extended by new classes.}
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  definitions, and to be extended by new classes.}
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"externalptr" # raw external pointers for use in C code
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"externalptr" # raw external pointers for use in C code
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"ANY"  # virtual classes used by the methods package itself
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"ANY"  # virtual classes used by the methods package itself
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"VIRTUAL"
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"VIRTUAL"
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"missing"
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"missing"
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"namedList" # the alternative to "list" that preserves the names attribute
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}
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}
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\section{Objects from the Classes}{
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\section{Objects from the Classes}{
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  Objects can be created by calls of the form \code{new(Class, ...)},
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  Objects can be created by calls of the form \code{new(Class, ...)},
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  where \code{Class} is the quoted class name, and the remaining
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  where \code{Class} is the quoted class name, and the remaining
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  arguments if any are objects to be interpreted as vectors of this
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  arguments if any are objects to be interpreted as vectors of this
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  class.  Multiple arguments will be concatenated.
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  class.  Multiple arguments will be concatenated.
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  The class \code{"expression"} is slightly odd, in that the \dots
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  The class \code{"expression"} is slightly odd, in that the \dots
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  arguments will \emph{not} be evaluated; therefore, don't enclose them
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  arguments will \emph{not} be evaluated; therefore, don't enclose them
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  in a call to \code{quote()}.
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  in a call to \code{quote()}.
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  Note that class \code{"list"} is a pure vector.  Although lists with
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  names go back to the earliest versions of S, they are an extension
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  of the vector concept in that they have an attribute (which can now
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  be a slot) and which is either \code{NULL} or a character vector of
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  the same length as the vector.  If you want to guarantee that list
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  names are preserved, use class \code{"namedList"}, rather than
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  \code{"list"}.  Objects from this class must have a names attribute,
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  corresponding to slot \code{"names"},
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  of type \code{"character"}.  Internally, R treats names for
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  lists  specially, which makes it impractical to have the corresponding slot in
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  class \code{"namedList"} be a union of character names and \code{NULL}.
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}
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}
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\section{Classes and Types}{
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The basic classes include classes for the basic R types.  Note that
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objects of these types will not usually be S4 objects
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(\code{\link{isS4}} will return \code{FALSE}), although objects from
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classes that contain the basic class will be S4 objects, still with
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the same type.  The type as
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returned by \code{\link{typeof}} will sometimes differ from the class,
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either just from a choice of terminology (type \code{"symbol"} and
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class \code{"name"}, for example) or because there is not a one-to-one
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correspondence between class and type (most of the classes that
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inherit from class \code{"language"} have type \code{"language"}, for example).
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}
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\section{Extends}{
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\section{Extends}{
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  Class \code{"vector"}, directly.
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  The vector classes extend \code{"vector"}, directly.
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}
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}
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\section{Methods}{
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\section{Methods}{
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  \describe{
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  \describe{
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    \item{coerce}{Methods are defined to coerce arbitrary objects to
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    \item{coerce}{Methods are defined to coerce arbitrary objects to
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      these classes, by calling the corresponding basic function, for
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      the vector classes, by calling the corresponding basic function, for
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      example, \code{as(x, "numeric")} calls \code{as.numeric(x)}. }
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      example, \code{as(x, "numeric")} calls \code{as.numeric(x)}. }
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  }
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  }
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}
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}
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\keyword{classes}
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\keyword{classes}