R: Tools for Managing Generic Functions

GenericFunctions {methods} | R Documentation

## Tools for Managing Generic Functions

### Description

The functions documented here manage collections of methods associated with a generic function, as well as providing information about the generic functions themselves.

### Usage

    isGeneric(f, where, fdef, getName = FALSE)

    isGroup(f, where, fdef)

    removeGeneric(f, where)

    standardGeneric(f)

    dumpMethod(f, signature, file, where, def)

    existsFunction(f, generic = TRUE, where)

    findFunction(f, generic=TRUE)

    dumpMethods(f, file, signature, methods, where)

    signature(...)

    removeMethods(f, where)

    setReplaceMethod(f, ...)

    getGenerics(where)

    allGenerics(where)

    callGeneric(...)

### Arguments

`f` | The character string naming the function.
`where` | Where on the search list of attached packages to look for functions or methods. By default, use the whole search list to find the relevant object(s).
`signature` | The class signature of the relevant method. A signature is a named or unnamed vector of character strings. If named, the names must be formal argument names for the generic function. If `signature` is unnamed, the default is to use the first `length(signature)` formal arguments of the function.
`file` | The file on which to dump method definitions.
`def` | The function object defining the method; if omitted, the current method definition corresponding to the signature.
`...` | Named or unnamed arguments to form a signature.
`generic` | In testing or finding functions, should generic functions be included. Supply as `FALSE` to get only non-generic functions.
`fdef` | Optional, the generic function definition. Usually omitted in calls to `isGeneric`
`getName` | If `TRUE`, `isGeneric` returns the name of the generic. By default, it returns `TRUE`.
`methods` | The methods object containing the methods to be dumped. By default, the methods defined for this generic (optionally on the specified `where` location).

### Summary of Functions

`isGeneric`:
  Is there a function named `f`, and if so, is it a generic?

  The `getName` argument allows a function to find the name from a function definition. If it is `TRUE` then the name of the generic is returned, or `FALSE` if this is not a generic function definition.

  The behavior of `isGeneric` and `getGeneric` for primitive functions is slightly different. These functions don't exist as formal function objects (for efficiency and historical reasons), regardless of whether methods have been defined for them. A call to `isGeneric` tells you whether methods have been defined for this primitive function, either on database `where` or anywhere in the current search list. In contrast, a call to `getGeneric` will return what the generic for that function would be, even if no methods have been currently defined for it.

`removeGeneric`:
  Remove the generic function of this name.
`standardGeneric`:
  Dispatches a method from the current function call for the generic function `fname`.

`getMethods`:
  The list of methods for the specified generic.

`dumpMethod`:
  Dump the method for this generic function and signature.

`existsFunction`:
  Is there a function of this name. If `generic==FALSE`, generic functions are not counted.

`findFunction`:
  return all the elements of the search list on which a function definition for `name` exists.

  NOTE: Use this rather than `find` with `mode="function"`, which is not as meaningful, and has a few subtle bugs from its use of regular expressions.

`selectMethod`:
  Returns the method (a function) that R would use to evaluate a call to this generic, with arguments corresponding to the specified signature.

  f = the name of the generic function sig = the signature of classes to match to the arguments of f.

`dumpMethods`:
  Dump all the methods for this generic.
`signature`:
  Returns a named list of classes to be matched to arguments of a generic function.

`callGeneric`:
  In the body of a method, this function will make a call to the current generic function. If no arguments are passed to `callGeneric`, the arguments to the current call are passed down; otherwise, the arguments are interpreted as in a call to the generic function.

### Details

`setGeneric`:

  If there is already a non-generic function of this name, it will be used to define the generic unless `def` is supplied, and the current function will become the default method for the generic.

  If `def` is supplied, this defines the generic function, and no default method will exist (often a good feature, if the function should only be available for a meaningful subset of all objects).

  Arguments `group` and `valueClass` are retained for consistency with S-Plus, but are currently not used.

`isGeneric`:

  If the `fdef` argument is supplied, take this as the definition of the generic, and test whether it is really a generic, with `f` as the name of the generic. (This argument is not available in S-Plus.)

`removeGeneric`:

  If `where` supplied, just remove the version on this element of the search list; otherwise, removes the first version encountered.

`standardGeneric`:

  Generic functions should usually have a call to `standardGeneric` as their entire body. They can, however, do any other computations as well.

  The usual `setGeneric` (directly or through calling `setMethod`) creates a function with a call to `standardGeneric`.

`getMethods`:
  If the function is not a generic function, returns NULL. The `f` argument can be either the character string name of the generic or the object itself

  The `where` argument optionally says where to look for the function, if `f` is given as the name.

`dumpMethod`:

  The resulting source file will recreate the method.

`findFunction`:
  If `generic` is FALSE, ignore generic functions.

`selectMethod`:
  The vector of strings for the classes can be named or not. If named, the names must match formal argument names of f. If not named, the signature is assumed to apply to the arguments of f in order. mustFind = If TRUE, an error results if there is no method (or no unique method) corresponding to this signature. Otherwise may return NULL or a MethodsList object.

`dumpMethods`:

  If `signature` is supplied only the methods matching this initial signature are dumped. (This feature is not found in S-Plus: don't use it if you want compatibility.)

`signature`:
  The advantage of using `signature` is to provide a check on which arguments you meant, as well as clearer documentation in your method specification. In addition, `signature` checks that each of the elements is a single character string.

`removeMethods`:
  Returns `TRUE` if `f` was a generic function, `FALSE` (silently) otherwise.

  If there is a default method, the function will be re-assigned as a simple function with this definition; otherwise, it will be removed. The assignment or removal can be controlled by optional argument `where`, which defaults to the first element of the search list having a function called `f`.

### Author(s)

John Chambers

### 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

`setGeneric`, `setClass`, `showMethods`

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