getClass
Get Class Definition
Get the definition of a class.
- Keywords
- classes, programming
Usage
getClass (Class, .Force = FALSE, where)
getClassDef(Class, where, package, inherits = TRUE)Arguments
- Class
the character-string name of the class, often with a
"package"attribute as noted below underpackage.- .Force
if
TRUE, returnNULLif the class is undefined; otherwise, an undefined class results in an error.- where
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.
- package
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 theClassargument is used, if any. There will usually be a package attribute ifClasscomes fromclass(x)for some object.- inherits
logical; should the class definition be retrieved from any enclosing environment and also from the cache? If
FALSEonly a definition in the environmentwherewill be returned.
Details
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
Value
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.
References
Chambers, John M. (2016) Extending R, Chapman & Hall. (Chapters 9 and 10.)
See Also
Examples
library(methods)
# 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"))
# }