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Get the definition of a class.
getClass (Class, .Force = FALSE, where)
getClassDef(Class, where, package, inherits = TRUE)the character-string name of the class, often with a
"package" attribute as noted below under package.
if TRUE, return NULL if the class is
undefined; otherwise, an undefined class results in an error.
environment from which to begin the search for the definition; by default, start at the top-level (global) environment and proceed through the search list.
the name of the package asserted to hold the
definition. If it is a non-empty string it is used instead of
where, as the first place to look for the class.
Note that the package must be loaded but need not be attached. By
default, the package attribute of the Class argument is
used, if any. There will usually be a package attribute if
Class comes from class(x) for some object.
logical; should the class definition be retrieved from
any enclosing environment and also from the cache? If FALSE
only a definition in the environment where will be returned.
The object defining the class. If the class definition is not found,
getClassDef returns NULL, while getClass, which
calls getClassDef, either generates an error or, if
.Force is TRUE, returns a simple definition for the
class. The latter case is used internally, but is not typically
sensible in user code.
The non-null returned value is an object of class
'>classRepresentation.
Use functions such as setClass and
setClassUnion to create class definitions.
Class definitions are stored in metadata objects in a package
namespace or other environment where they are defined. When
packages are loaded, the class definitions in the package are cached in an internal
table. Therefore, most calls to getClassDef will find the
class in the cache or fail to find it at all, unless inherits
is FALSE, in which case only the environment(s) defined by
package or where are searched.
The class cache allows for multiple definitions of the same class name in separate environments, with of course the limitation that the package attribute or package name must be provided in the call to
Chambers, John M. (2016) Extending R, Chapman & Hall. (Chapters 9 and 10.)
# NOT RUN {
getClass("numeric") ## a built in class
cld <- getClass("thisIsAnUndefinedClass", .Force = TRUE)
cld ## a NULL prototype
## If you are really curious:
utils::str(cld)
## Whereas these generate errors:
try(getClass("thisIsAnUndefinedClass"))
try(getClassDef("thisIsAnUndefinedClass"))
# }
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