\HeaderA{findClass}{Computations with Classes}{findClass}
\aliasA{getClasses}{findClass}{getClasses}
\aliasA{isClass}{findClass}{isClass}
\aliasA{removeClass}{findClass}{removeClass}
\aliasA{resetClass}{findClass}{resetClass}
\aliasA{sealClass}{findClass}{sealClass}
\keyword{programming}{findClass}
\keyword{classes}{findClass}
\keyword{methods}{findClass}
\begin{Description}\relax
Functions to find and manipulate class definitions.
\end{Description}
\begin{Usage}
\begin{verbatim}
removeClass(Class, where)

isClass(Class, formal=TRUE, where)

getClasses(where, inherits = missing(where))

findClass(Class, where, unique = "")

resetClass(Class, classDef, where)

sealClass(Class, where)

\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{Class}] character string name for the class.  The functions will
usually take a class definition instead of the string.  To restrict
the class to those defined in a particular package, set the
\code{\LinkA{packageSlot}{packageSlot}} of the character string.
\item[\code{where}] The
environment in which to modify or remove the
definition.  Defaults to the top-level environment of the calling function
(the global environment for ordinary computations, but the
environment or name space of a package in the source for a package).

When searching for class definitions, \code{where} defines where to
do the search, and the default is to search from the top-level
environment or name space of the caller to this function.

\item[\code{unique}] if \code{findClass} expects a unique location for the
class, \code{unique} is a character string explaining the purpose
of the search (and is used in warning and error messages).  By
default, multiple locations are possible and the function always
returns a list.

\item[\code{inherits}] in a call to \code{getClasses}, should the value
returned include all parent environments of \code{where}, or that
environment only?  Defaults to \code{TRUE} if \code{where} is
omitted, and to \code{FALSE} otherwise.

\item[\code{formal}] Should a formal definition be required? 
\item[\code{classDef}] For \code{removeClass}, the optional class
definition (but usually it's better for \code{Class} to be the
class definition, and to omit \code{classDef}).

\end{ldescription}
\end{Arguments}
\begin{Details}\relax
These are the functions that test and manipulate formal class
definitions.  Brief documentation is provided below.  See the
references for an introduction and for more details.

\describe{
\item[\code{removeClass}:] Remove the definition of this class, from the environment
\code{where} if this argument is supplied; if not,
\code{removeClass} will search for a definition, starting in the
top-level environment of the call to \code{removeClass}, and
remove the (first) definition found.

\item[\code{isClass}:] Is this the name of a formally defined class? (Argument
\code{formal} is for compatibility and is ignored.)

\item[\code{getClasses}:] The names of all the classes formally defined on \code{where}.  If
called with no argument, all the classes visible from the
calling function (if called from the top-level, all the classes
in any of the environments on the search list).  The
\code{inherits} argument can be used to search a particular
environment and all its parents, but usually the default setting
is what you want.

\item[\code{findClass}:] The list of environments or positions on the search list in
which a class definition of \code{Class} is found.  If
\code{where} is supplied, this is an environment (or name space)
from which the search takes place; otherwise the top-level
environment of the caller is used.  If \code{unique} is supplied
as a character string, \code{findClass} returns a single
environment or position.  By default, it always returns a list.
The calling function should select, say, the first element as a
position or environment for functions such as \code{\LinkA{get}{get}}.

If \code{unique} is supplied as a character string,
\code{findClass} will warn if there is more than one definition
visible (using the string to identify the purpose of the call),
and will generate an error if no definition can be found.

\item[\code{resetClass}:] Reset the internal definition of a class.  Causes the complete
definition of the class to be re-computed, from the
representation and superclasses specified in the original
call to \code{setClass}.

This function is called when aspects of the class definition are
changed.  You would need to call it explicitly if you changed the
definition of a class that this class extends (but doing that in
the  middle of a session is living dangerously, since it may
invalidate existing objects).

\item[\code{sealClass}:] Seal the current definition of the specified
class, to prevent further changes.  It is possible to seal a class
in the call to \code{setClass}, but sometimes further changes have
to be made (e.g., by calls to \code{setIs}).  If so, call
\code{sealClass} after all the relevant changes have been made.

}
\end{Details}
\begin{References}\relax
Chambers, John M. (2008)
\emph{Software for Data Analysis: Programming with R}
Springer.  (For the R version.)

Chambers, John M. (1998)
\emph{Programming with Data}
Springer (For the original S4 version.)
\end{References}
\begin{SeeAlso}\relax
\code{\LinkA{setClassUnion}{setClassUnion}},
\code{\LinkA{Methods}{Methods}},
\code{\LinkA{makeClassRepresentation}{makeClassRepresentation}}
\end{SeeAlso}

