| isSealedMethod {methods} | R Documentation |
These functions check for either a method or a class that has been “sealed” when it was defined, and which therefore cannot be re-defined.
isSealedMethod(f, signature, fdef, where) isSealedClass(Class, where)
f |
The quoted name of the generic function. |
signature |
The class names in the method's signature, as
they would be supplied to setMethod. |
fdef |
Optional, and usually omitted: the generic function
definition for f. |
Class |
The quoted name of the class. |
where |
where to search for the method or class definition. By
default, searches from the top environment of the call to
isSealedMethod or isSealedClass, typically the
global environment or the namespace of a package containing a call
to one of the functions. |
In the R implementation of classes and methods, it is possible to seal the definition of either a class or a method. The basic classes (numeric and other types of vectors, matrix and array data) are sealed. So also are the methods for the primitive functions on those data types. The effect is that programmers cannot re-define the meaning of these basic data types and computations. More precisely, for primitive functions that depend on only one data argument, methods cannot be specified for basic classes. For functions (such as the arithmetic operators) that depend on two arguments, methods can be specified if one of those arguments is a basic class, but not if both are.
Programmers can seal other class and method definitions by using the
sealed argument to setClass or setMethod.
The functions return FALSE if the method or class is not
sealed (including the case that it is not defined); TRUE if
it is.
The R package methods implements, with a few exceptions, the programming interface for classes and methods in the book Programming with Data (John M. Chambers, Springer, 1998), in particular sections 1.6, 2.7, 2.8, and chapters 7 and 8.
While the programming interface for the methods package follows the reference, the R software is an original implementation, so details in the reference that reflect the S4 implementation may appear differently in R. Also, there are extensions to the programming interface developed more recently than the reference. For a discussion of details and ongoing development, see the web page http://developer.r-project.org/methodsPackage.html and the pointers from that page.
## these are both TRUE
isSealedMethod("+", c("numeric", "character"))
isSealedClass("matrix")
setClass("track",
representation(x="numeric", y="numeric"))
## but this is FALSE
isSealedClass("track")
## and so is this
isSealedClass("A Name for an undefined Class")
## and so are these, because only one of the two arguments is basic
isSealedMethod("+", c("track", "numeric"))
isSealedMethod("+", c("numeric", "track"))