setStage: Define a Stage Class
In tengfei/commandr: Command pattern in R

Description Usage Arguments Details Value Author(s) See Also Examples

This function defines new derivatives of the Stage class. It is a wrapper around setClass and thus has a similar interface.

1 2	setStage(name, dispname = name, intype = "ANY", outtype = intype, where = topenv(parent.frame()))

`name`	The name of the stage, i.e., the role string
`dispname`	The name for display in a user interface
`intype`	The class of the data that protocols of this stage accept as input
`outtype`	The class of the data that protocols of this stage accept as output
`where`	The environment in which to define the stage class

Calling setStage defines two classes:

A derivative of Stage that represents this stage
A derivative of Protocol from which all protocols that implement this stage derive

For example, if we had a stage named “average”, calling setStage would create the classes StageAverage and ProtoAverage.

The function also defines a generic, named by the name argument, that performs a protocol of this stage. There is a method that takes an object of type intype as first argument and a method name as its second. Additional arguments are passed to the perform method of the protocol. In our prior example, there would be a generic called average and method average,numeric if intype was given as “numeric”.

It also defines a generic of the form nameProto that serves as an accessor for protocols of this stage. A method is defined for Pipeline and outtype, so that one could retrieve our “average” protocol with averageProto(pipeline) or averageProto(result). Similarly, a replacement generic and methods are defined.

The name of the role

Michael Lawrence

The Stage class; setProtocol for defining a new type of protocol

## simplest definition
setStage("average")
## add a display name and specialize to numeric input
setStage("average", "Average Vector", intype = "numeric")
setProtocol("mean", fun = mean, parent = "average")
setProtocol("quantile", representation = list(probs = "numeric"),
            fun = quantile, parent = "average")
setProtocol("range", representation = list(low = "numeric", high = "numeric"), 
            fun = function(x, low = 0, high = Inf) x[x >= low & x <= high],
            parent = setStage("trim", intype = "numeric"))

## Class Stage derivative
showClass("StageAverage")
## Class Protocol derivative
showClass("ProtoAverage")

## generic defined
showMethods("average")

# try this generic method
d <- c(1, 2, 4)
average(d, "mean")

## create a pipeline
p <- Pipeline("trim", "average")
res <- perform(p, d)
res
## generic *Proto
averageProto(p)
averageProto(res)