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

representation {methods} | R Documentation

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

### Description

In calls to `setClass`, these two functions construct, respectively, the `representation` and `prototype` arguments. They do various checks and handle special cases. You're encouraged to use them when defining classes that, for example, extend other classes as a data part or have multiple superclasses, or that combine extending a class and slots.

### 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 pf `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

The R package methods implements, with a few exceptions, the programming interface for classes and methods in the book Programming with Data (John M. Chambers, Springer, 1998), in particular sections 1.6, 2.7, 2.8, and chapters 7 and 8.

While the programming interface for the methods package follows the reference, the R software is an original implementation, so details in the reference that reflect the S4 implementation may appear differently in R. Also, there are extensions to the programming interface developed more recently than the reference. For a discussion of details see `?Methods` and the links from that documentation.

### 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")

    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 2.6.0 Index]