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R version 2.5.0 Under development (unstable) (2006-11-30 r40078)
Copyright (C) 2006 The R Foundation for Statistical Computing
ISBN 3-900051-07-0
R is free software and comes with ABSOLUTELY NO WARRANTY.
You are welcome to redistribute it under certain conditions.
Type 'license()' or 'licence()' for distribution details.
R is a collaborative project with many contributors.
Type 'contributors()' for more information and
'citation()' on how to cite R or R packages in publications.
Type 'demo()' for some demos, 'help()' for on-line help, or
'help.start()' for an HTML browser interface to help.
Type 'q()' to quit R.
> #### Testing UseMethod() and even more NextMethod()
> ####
>
> ###-- Group methods
>
> ## previous versions used print() and hit an auto-printing bug.
>
> ### Arithmetic "Ops" :
> ">.bar" <- function(...) {cat("using >.bar\n"); FALSE}
> ">.foo" <- function(...) {cat("using >.foo\n"); TRUE}
> Ops.foo <- function(...) {
+ cat("using Ops.foo\n")
+ NextMethod()
+ }
> Ops.bar <- function(...) {
+ cat("using Ops.bar\n")
+ TRUE
+ }
>
> x <- 2:4 ; class(x) <- c("foo", "bar")
> y <- 4:2 ; class(y) <- c("bar", "foo")
>
> ## The next 4 give a warning each about incompatible methods:
> x > y
[1] FALSE FALSE TRUE
Warning message:
Incompatible methods (">.foo", ">.bar") for ">"
> y < x # should be the same (warning msg not, however)
[1] FALSE FALSE TRUE
Warning message:
Incompatible methods ("Ops.bar", "Ops.foo") for "<"
> x == y
[1] FALSE TRUE FALSE
Warning message:
Incompatible methods ("Ops.foo", "Ops.bar") for "=="
> x <= y
[1] TRUE TRUE FALSE
Warning message:
Incompatible methods ("Ops.foo", "Ops.bar") for "<="
>
> x > 3 ##[1] ">.foo"
using >.foo
[1] TRUE
>
> rm(list=">.foo")
> x > 3 #-> "Ops.foo" and ">.bar"
using Ops.foo
using >.bar
[1] FALSE
>
>
>
> ### ------------ was ./mode-methods.R till R ver. 1.0.x ----------------
>
> ###-- Using Method Dispatch on "mode" etc :
> ## Tests S3 dispatch with the class attr forced to be data.class
> ## Not very relevant when S4 methods are around, but kept for historical interest
> abc <- function(x, ...) {
+ cat("abc: Before dispatching; x has class `", class(x), "':", sep="")
+ str(x)
+ UseMethod("abc", x) ## UseMethod("abc") (as in S) fails
+ }
>
> abc.default <- function(x, ...) sys.call()
>
> "abc.(" <- function(x)
+ cat("'(' method of abc:", deparse(sys.call(sys.parent())),"\n")
> abc.expression <- function(x)
+ cat("'expression' method of abc:", deparse(sys.call(sys.parent())),"\n")
>
> abc(1)
abc: Before dispatching; x has class `numeric': num 1
abc.default(1)
> e0 <- expression((x))
> e1 <- expression(sin(x))
> abc(e0)
abc: Before dispatching; x has class `expression': expression((x))
'expression' method of abc: abc.expression(e0)
> abc(e1)
abc: Before dispatching; x has class `expression': expression(sin(x))
'expression' method of abc: abc.expression(e1)
> abc(e0[[1]])
abc: Before dispatching; x has class `(': language, mode "(": (x)
'(' method of abc: `abc.(`(e0[[1]])
> abc(e1[[1]])
abc: Before dispatching; x has class `call': language sin(x)
abc.default(e1[[1]])
>
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