representation {methods} | R Documentation

## Construct a Representation or a Prototype for a Class Definition

### Description

These are old utility functions to construct, respectively a list designed to represent the slots and superclasses and a list of prototype specifications. The `representation()` function is no longer useful, since the arguments `slots` and `contains` to `setClass` are now recommended.

The `prototype()` function may still be used for the corresponding argument, but a simple list of the same arguments works as well.

### Usage

    representation(...)
    prototype(...)

### Arguments

`...`

The call to representation takes arguments that are single character strings. Unnamed arguments are classes that a newly defined class extends; named arguments name the explicit slots in the new class, and specify what class each slot should have.

In the call to `prototype`, if an unnamed argument is supplied, it unconditionally forms the basis for the prototype object. Remaining arguments are taken to correspond to slots of this object. It is an error to supply more than one unnamed argument.

### Details

The `representation` function applies tests for the validity of the arguments. Each must specify the name of a class.

The classes named don't have to exist when `representation` is called, but if they do, then the function will check for any duplicate slot names introduced by each of the inherited classes.

The arguments to `prototype` are usually named initial values for slots, plus an optional first argument that gives the object itself. The unnamed argument is typically useful if there is a data part to the definition (see the examples below).

### Value

The value of `representation` is just the list of arguments, after these have been checked for validity.

The value of `prototype` is the object to be used as the prototype. Slots will have been set consistently with the arguments, but the construction does not use the class definition to test validity of the contents (it hardly can, since the prototype object is usually supplied to create the definition).

### References

Chambers, John M. (2008) Software for Data Analysis: Programming with R Springer. (For the R version.)

Chambers, John M. (1998) Programming with Data Springer (For the original S4 version.)

### See Also

`setClass`

### Examples

    ## representation for a new class with a directly define slot "smooth"
    ## which should be a "numeric" object, and extending class "track"
    representation("track", smooth ="numeric")

    ###  >>> This *is* old syntax -- use 'contains=*, slots=*' instead <<<
    ###                ==========         ----------  ------   ======

    setClass("Character",representation("character"))
    setClass("TypedCharacter",representation("Character",type="character"),
              prototype(character(0),type="plain"))
    ttt <- new("TypedCharacter", "foo", type = "character")

    setClass("num1", representation(comment = "character"),
             contains = "numeric",
             prototype = prototype(pi, comment = "Start with pi"))

[Package methods version 3.4.2 Index]