R.oo (version 1.26.0)

extend: Extends a object

Description

via a mechanism known as "parasitic inheritance". 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 default
extend(this, ...className, ...)

Value

Returns an object of class ...className.

Arguments

this

Object to be extended.

...className

The name of new class.

...

Attribute fields of the new class.

Author

Henrik Bengtsson

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)