methods (version 3.3.1)

callGeneric: Call the Current Generic Function from a Method

Description

A call to callGeneric can only appear inside a method definition. It then results in a call to the current generic function. The value of that call is the value of callGeneric. While it can be called from any method, it is useful and typically used in methods for group generic functions.

Usage

callGeneric(...)

Arguments

...

Optionally, the arguments to the function in its next call.

If no arguments are included in the call to callGeneric, the effect is to call the function with the current arguments. See the detailed description for what this really means.

Value

The value returned by the new call.

Details

The name and package of the current generic function is stored in the environment of the method definition object. This name is looked up and the corresponding function called.

The statement that passing no arguments to callGeneric causes the generic function to be called with the current arguments is more precisely as follows. Arguments that were missing in the current call are still missing (remember that "missing" is a valid class in a method signature). For a formal argument, say x, that appears in the original call, there is a corresponding argument in the generated call equivalent to x = x. In effect, this means that the generic function sees the same actual arguments, but arguments are evaluated only once.

Using callGeneric with no arguments is prone to creating infinite recursion, unless one of the arguments in the signature has been modified in the current method so that a different method is selected.

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

GroupGenericFunctions for other information about group generic functions; Methods for the general behavior of method dispatch

Examples

## the method for group generic function Ops
## for signature( e1="structure", e2="vector")
function (e1, e2)
{
    value <- callGeneric(e1@.Data, e2)
    if (length(value) == length(e1)) {
        e1@.Data <- value
        e1
    }
    else value
}

## For more examples
## Not run: 
# showMethods("Ops", includeDefs = TRUE)
# ## End(Not run)