Extends a object

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.

# Default S3 method
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.

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)
})
#> NULL

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

x <- MyDouble(3.1415926)
print(x)
#> [1] "3.141593"

x <- MyDouble(3.1415926, fmtstr="%3.2f")
print(x)
#> [1] "3.14"
attr(x, "fmtstr") <- "%e"
print(x)
#> [1] "3.141593e+00"






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)
})
#> NULL

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

x <- MyList(3.1415926)
print(x)
#> [1] "3.141593"
x <- MyList(3.1415926, fmtstr="%3.2f")
print(x)
#> [1] "3.14"
x$fmtstr <- "%e"
print(x)
#> [1] "3.141593e+00"