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Register an old-style (a.k.a. `S3') class as a formally defined
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Register an old-style (a.k.a. `S3') class as a formally defined
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class. The \code{Classes} argument is the character vector used as the
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class. The \code{Classes} argument is the character vector used as the
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\code{class} attribute; in particular, if there is more than one
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\code{class} attribute; in particular, if there is more than one
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string, old-style class inheritance is mimiced. Registering via
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string, old-style class inheritance is mimiced. Registering via
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\code{setOldClass} allows S3 classes to appear in method
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\code{setOldClass} allows S3 classes to appear in method
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signatures, and in class inheritance if a prototype is included.
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signatures, and as a slot in an S4 class if a prototype is included.
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}
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}
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\usage{
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\usage{
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setOldClass(Classes, prototype, where, test = FALSE)
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setOldClass(Classes, prototype, where, test = FALSE)
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}
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}
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\arguments{
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\arguments{
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A character vector, giving the names for old-style
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A character vector, giving the names for old-style
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classes, as they would appear on the right side of an assignment of
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classes, as they would appear on the right side of an assignment of
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the \code{class} attribute.
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the \code{class} attribute.
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}
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}
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\item{prototype}{
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\item{prototype}{
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An optional object to use as the prototype. This should be provided as the default S3 object for the class, if you plan to use the class as a slot or superclass in an S4 class. See the details section.
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An optional object to use as the prototype. This should be provided as the default S3 object for the class, if you plan to use the class as a slot in an S4 class. See the details section.
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}
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}
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\item{where}{
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\item{where}{
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Where to store the class definitions, the global or top-level
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Where to store the class definitions, the global or top-level
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environment by default. (When either function is called in the
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environment by default. (When either function is called in the
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source for a package, the class definitions will be included in the
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source for a package, the class definitions will be included in the
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Each of the names will be defined as an S4 class, extending the
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Each of the names will be defined as an S4 class, extending the
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remaining classes in \code{Classes}, and the class
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remaining classes in \code{Classes}, and the class
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\code{oldClass}, which is the \dQuote{root} of all old-style classes.
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\code{oldClass}, which is the \dQuote{root} of all old-style classes.
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S3 classes have no formal definition, and therefore no formally defined slots.
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S3 classes have no formal definition, and therefore no formally defined slots.
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If a \code{prototype} argument is supplied in the call to \code{setOldClass()}, objects from the class can be generated.
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If a \code{prototype} argument is supplied in the call to \code{setOldClass()}, objects from the class can be generated.
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If the S3 class is to be extended by an S4 class or a slot in an S4 class, providing a prototype is recommended.
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If the S3 class is to be a slot in an S4 class, providing a prototype is recommended.
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Otherwise, the class will be created as a virtual S4 class; method dispatch will still work and inheritance will follow the S3 class hierarchy, but actions that require a prototype object from the class will not.
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Otherwise, the class will be created as a virtual S4 class; method dispatch will still work and inheritance will follow the S3 class hierarchy, but actions that require a prototype object from the class will not.
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For example, using the class as a slot in an S4 class definition will set the corresponding slot to \code{NULL} in the prototype for the S4 class.
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For example, using the class as a slot in an S4 class definition will set the corresponding slot to \code{NULL} in the prototype for the S4 class.
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Providing a prototype allows the function \code{new()} to be called for this class, but optional arguments in this call are not meaningful, since the class has no formal slots.
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Providing a prototype allows the function \code{new()} to be called for this class, but optional arguments in this call are not meaningful, since the class has no formal slots.
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Extending an S3 class with an S4 class is formally legal, but discouraged.
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Extending an S3 class with an S4 class is formally legal, but discouraged.
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