Functions to find classes:
isClass tests for a class;
findClass returns the name(s) of packages containing the
getClasses returns the names of all the classes in an
environment, typically a namespace. To examine the definition of a class, use
isClass(Class, formal=TRUE, where)
getClasses(where, inherits = missing(where))
findClass(Class, where, unique = "")
## The remaining functions are retained for compatibility ## but not generally recommended
resetClass(Class, classDef, where)
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
packageSlot of the character string.
environment in which to search for
the class definition. Defaults to the top-level environment of the
calling function. When called from the command line, this has the
effect of using all the package environments in the search list.
To restrict the search to classes in a particular package, use
pkg the package name; to restrict
the exported classes, use
where = "package:pkg" after the
package is attached to the search list.
logical is a formal definition
required? For S compatibility, and always treated as
findClass expects a unique location for the
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.
in a call to
getClasses, should the value
returned include all parent environments of
where, or that
environment only? Defaults to
omitted, and to
resetClass, the optional class
Is this the name of a formally defined class?
The names of all the classes formally defined on
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
where argument is used to search only in a particular package.
The list of environments in
which a class definition of
Class is found. If
where is supplied, a list is still returned, either empty
or containing the environment corresponding to
By default when called from the R session, the global
environment and all the currently
attached packages are searched.
unique is supplied as a character string,
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.
The remaining functions are retained for back-compatibility and internal use, but not generally recommended.
Remove the definition of this class. This can't be used if the class is in another package, and would rarely be needed in source code defining classes in a package.
Reset the internal definition of a class. Not legitimate for a class definition not in this package and rarely needed otherwise.
Seal the current definition of the specified class, to prevent further changes, by setting the corresponding slot in the class definition. This is rarely used, since classes in loaded packages are sealed by locking their namespace.
Chambers, John M. (2016) Extending R, Chapman & Hall. (Chapters 9 and 10.)
Chambers, John M. (2008) Software for Data Analysis: Programming with R Springer. (Chapter 9 has some details not in the later reference.)