methods (version 3.5.3)

isSealedMethod: Check for a Sealed Method or Class

Description

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.

Usage

isSealedMethod(f, signature, fdef, where)
isSealedClass(Class, where)

Arguments

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.

Value

The functions return FALSE if the method or class is not sealed (including the case that it is not defined); TRUE if it is.

Details

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.

References

Chambers, John M. (2008) Software for Data Analysis: Programming with R Springer. (For the R version.)

Chambers, John M. (1998) Programming with Data Springer (For the original S4 version.)

Examples

# NOT RUN {
## these are both TRUE
isSealedMethod("+", c("numeric", "character"))
isSealedClass("matrix")

setClass("track", slots = c(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"))

# }