R.oo (version 1.7.5)

extend: Extends a object

Description

Simply speaking this method "extends" the class of an object. What is actually happening is that it creates an instance of class name ...className, by taking another object and add ...className to the class list and also add all the named values in ... as attributes. The method should be used by the constructor of a class and nowhere else.

Usage

## S3 method for class 'default':
extend(this, ...className, ...)

Arguments

this

Object to be extended.

...className

The name of new class.

...

Attribute fields of the new class.

Value

• Returns an object of class ...className.

Examples

setConstructorS3("MyDouble", function(value=0, ...) {
  extend(as.double(value), "MyDouble", ...)
})

setMethodS3("as.character", "MyDouble", function(object, ...) {
  fmtstr <- attr(object, "fmtstr")
  if (is.null(fmtstr))
    fmtstr <- "%.6f"
  sprintf(fmtstr, object)
})

setMethodS3("print", "MyDouble", function(object, ...) {
  print(as.character(object), ...)
})

x <- MyDouble(3.1415926)
print(x)

x <- MyDouble(3.1415926, fmtstr="%3.2f")
print(x)
attr(x, "fmtstr") <- "%e"
print(x)






setConstructorS3("MyList", function(value=0, ...) {
  extend(list(value=value, ...), "MyList")
})

setMethodS3("as.character", "MyList", function(object, ...) {
  fmtstr <- object$fmtstr
  if (is.null(fmtstr))
    fmtstr <- "%.6f"
  sprintf(fmtstr, object$value)
})

setMethodS3("print", "MyList", function(object, ...) {
  print(as.character(object), ...)
})

x <- MyList(3.1415926)
print(x)
x <- MyList(3.1415926, fmtstr="%3.2f")
print(x)
x$fmtstr <- "%e"
print(x)