new {methods}R Documentation

Generate an Object from a Class

Description

Given the name or the definition of a class, plus optionally data to be included in the object, new returns an object from that class.

Usage

new(Class, ...)

initialize(.Object, ...)

Arguments

Class Either the name of a class (the usual case) or the object describing the class (e.g., the value returned by getClass).
... Data to include in the new object. Named arguments correspond to slots in the class definition. Unnamed arguments must be objects from classes that this class extends.
.Object An object: see the Details section.

Details

The function new begins by copying the prototype object from the class definition. Then information is inserted according to the ... arguments, if any.

The interpretation of the ... arguments can be specialized to particular classes, if an appropriate method has been defined for the generic function "initialize". The new function calls initialize with the object generated from the prototype as the .Object argument to initialize.

By default, unnamed arguments in the ... are interpreted as objects from a superclass, and named arguments are interpreted as objects to be assigned into the correspondingly named slots. Thus, explicit slots override inherited information for the same slot, regardless of the order in which the arguments appear.

The initialize methods do not have to have ... as their second argument (see the examples), and generally it is better design not to have ... as a formal argument, if only a fixed set of arguments make sense.

For examples of initialize methods, see initialize-methods for existing methods for classes "traceable" and "environment", among others.

Note that the basic vector classes, "numeric", etc. are implicitly defined, so one can use new for these classes.

References

The web page http://www.omegahat.org/RSMethods/index.html is the primary documentation.

The functions in this package emulate the facility for classes and methods described in Programming with Data (John M. Chambers, Springer, 1998). See this book for further details and examples.

See Also

Classes

Examples

## using the definition of class "track" from Classes



## a new object with two slots specified
t1 <- new("track", x = seq(along=ydata), y = ydata)

# a new object including an object from a superclass, plus a slot
t2 <- new("trackCurve", t1, smooth = ysmooth)

### define a method for initialize, to ensure that new objects have
### equal-length x and y slots.

setMethod("initialize",
          "track",
          function(.Object, x = numeric(0), y = numeric(0)) {
            if(nargs() > 1) {
              if(length(x) != length(y))
                stop("specified x and y of different lengths")
              .Object@x <- x
              .Object@y <- y
            }
            .Object
          })

### the next example will cause an error (x will be numeric(0)),
### because we didn't build in defaults for x,
### although we could with a more elaborate method for initialize

try(new("track", y = sort(rnorm(10))))

## a better way to implement the previous initialize method.
## Why?  By using callNextMethod to call the default initialize method
## we don't inhibit classes that extend "track" from using the general
## form of the new() function.  In the previous version, they could only
## use x and y as arguments to new, unless they wrote their own
## intialize method.

setMethod("initialize", "track", function(.Object, ...) {
    .Object <- callNextMethod()
    if(length(.Object@x) != length(.Object@y))
     stop("specified x and y of different lengths")
    .Object
  })


[Package methods version 2.1.0 Index]