### Name: Methods
### Title: General Information on Methods
### Aliases: Methods
### Keywords: programming classes methods

### ** Examples

## The rules for inheriting S3 methods.

f3 <- function(x)UseMethod("f3") # an S3 generic to illustrate inheritance

## A class that extends a registered S3 class inherits that class' S3
## methods.  The S3 methods will be passed an object with the S3 class

setClass("myFrame", contains = "data.frame",
    representation(date = "POSIXt", type = "character"))

df1 <- data.frame(x = 1:10, y = rnorm(10), z = sample(letters,10))

mydf1 <- new("myFrame", df1, date = Sys.time())

## "myFrame" objects inherit "data.frame" S3 methods; e.g., for `[`

mydf1[1:2, ] # a data frame object (with extra attributes "date" and "type")

## Don't show: 

m1 <- mydf1[1:2,]
attr(m1, "date") <- attr(m1, "type") <- NULL
stopifnot(identical(m1, df1[1:2,]))
## End Don't show

## Extending an S3 class with inconsistent (instance-based) inheritance
setClass("myDateTime", contains = "POSIXt")

now <- Sys.time() # class(now) is c("POSIXt", "POSIXct")
nowLt <- as.POSIXlt(now)# class(nowLt) is c("POSIXt", "POSIXlt")

mCt <- new("myDateTime", now)
mLt <- new("myDateTime", nowLt)

## S3 methods will be selected using instance-based information

f3.POSIXct <- function(x) "The POSIXct result"
f3.POSIXlt <- function(x) "The POSIXlt result"

stopifnot(identical(f3(mCt), f3.POSIXct(mCt)))
stopifnot(identical(f3(mLt), f3.POSIXlt(mLt)))


## An S4 class that does not contain a registered S3 class or object type
## selects S3 methods according to its S4 "inheritance"
## but only if the class definition requests this via S3methods=TRUE
## ( from version 2.9.1 on)

setClass("classA", contains = "numeric",
   representation(realData = "numeric"), S3methods = TRUE)

Math.classA <- function(x) {(getFunction(.Generic))(x@realData)}

x <- new("classA", log(1:10), realData = 1:10)

stopifnot(identical(abs(x), 1:10))

setClass("classB", contains = "classA")

y <- new("classB", x)

stopifnot(identical(abs(y), 1:10)) # (version 2.9.0 or earlier fails here)

## Note: with a class that tries to combine both S3 and S4 superclasses.
## The S3 inheritance is used and the S3 method for
## the S4 superclass will not be selected.

setClass("classC", representation(x = "numeric"))

# an S3 method for "[" (not a good idea, but it would work)
`[.classc` <- function(x, ..., drop = TRUE) {x@x[...]}

setClass("classD", contains = c("classC", "data.frame"))

## by the rule mentioned in the S3 method section, the
## S3 methods are selected from the S3 class defined; that is, "data.frame"
## If the user expected to inherit `[.classC`, no luck.
xd <- new("classD", df1, x = 1:50)

## Note the error from `[.data.frame`
try(xd[1:25])

## Don't show: 
removeClass("classA"); removeClass("classB"); rm(x,y)
removeClass("myDateTime")
## End Don't show