Enum-class: Enumerated types

In objectProperties: A Factory of Self-Describing Properties

Enumerated types

Description

R functions often have parameters with enumerated values. These are typically passed as a character vector and resolved using match.arg(). The Enum structure is very similar to that of a factor, except the data is character, not integer and with appropriate validation.

Usage

setSingleEnum(prefix, levels, contains=character(),
              where=topenv(parent.frame()))

## S4 method for signature 'Enum'
levels(x)

Arguments

prefix	Prefix for new subclass of SingleEnum or MultipleEnum, e.g. if prefix is "Geom", the new subclass name would be GeomSingleEnum after calling setSingleEnum.
levels	An vector of characters which define the levels for this class.
contains	What class does this class extended besides SingleEnum.
where	the environment in which to store or remove the definition. Defaults to the top-level environment of the calling function.
x	A Enum object.

Details

The SingleEnum object is different from simple factor. It validates the value to see if it's in the defined levels during construction. and only the value within defined levels is allowed to be set as current chosen value when it is created as property. It is particularly useful for GUI design, such as creating a drop list or ratio buttons for exclusive choice, you can only choose one item within certain choices at one time. setSingleEnum will create a S4 subclass for SingleEnum, and return the class name.

The MultipleEnum has the same design with SingleEnum, except it support multiple choices. So for GUI level, it could be used for creating check boxes. setMultipleEnum will create a S4 subclass for MultipleEnum, and return the class name.

The Enum class is a Class union for SingleEnum and MultipleEnum

Color class is a special character, this properties could be used for creating a widgets which showing a color picker pallete and a text input field, a simple character object will be only treated as simple text in the UI. Color class could be constructed by constructor Color.

ColorEnum class is a VIRTUAL class, which including a set of SingleEnum subclass, when creating widget based on this property, it should be treated as a special color droplist, instead of showing a droplist of levels of text, it shows a drop list of colors, the levels are treated as color in this class. setColorEnum is a convenient class generator function for single enum of ColorEnum and it return a class name.

GlyphEnum class is a VIRTUAL class, which including a set of SingleEnum subclass, when creating widget based on this property, it should be treated as a special glyph droplist, instead of showing a droplist of levels of text, it shows a drop list of different glyphs, the levels are treated as glyphs in this class. Different engine genenerate icons for different glyphs, such as different point size, line type, etc. setGlyphEnum is a convenient class generator function for single enum of GlyphEnum and it return a class name.

Value

setSingleEnum return a class name for SingleEnum subclass.setMultipleEnum return a class name for MultipleEnum subclass. setColorEnum return a class name for ColorEnum subclass which is also a SingleEnum. setGlyphEnum return a class name for GlyphEnum subclass which is also a SingleEnum. All those function return a generator function in R(>= 2.15)

Author(s)

Tengfei Yin, Michael Lawrence

Examples

## ----------------------------------------------------------------------
##                   setSingleEnum
## ----------------------------------------------------------------------
ShapeEnum.gen <- setSingleEnum("Shape",
                                levels = c("circle", "line", "rectangle"))

obj <- new("ShapeSingleEnum", "circle")
obj
obj <- "triangle" # doesn't check, because it's not signal field.
obj # it's not SingleEnum object anymore, be careful.
class(obj) # just character

## only set it as properties, allow you to assign the value and
## validate it.
par.gen <- setRefClass("Graph",
                       properties(fields = list(shape = "ShapeSingleEnum"),
                                  prototype = list(shape = new("ShapeSingleEnum",
                                                     "circle"))))
pars <- par.gen$new()
pars$shape
pars$shape <- "line"
pars$shape
class(pars$shape)# still a SingleEnum
## ----------------------------------------------------------------------
##                   setMultipleEnum
## ----------------------------------------------------------------------
ShapeEnum.gen <- setMultipleEnum("Shape",
                                levels = c("circle", "line", "rectangle"))

par.gen <- setRefClass("Graph",
                       properties(list(shape = "ShapeMultipleEnum")))
## we can initialize in this way too
pars <- par.gen$new(shape = new("ShapeMultipleEnum", c("circle", "line")))
pars$shape
pars$shape <- c("line", "rectangle")
pars$shape
class(pars$shape)# still a MultipleEnum

## Color Single Enum
bgColorSingleEnum.gen <- setColorEnum("bgColor", levels = c("black", "white", "gray"))
obj <- new("bgColorSingleEnum", "white")
## Glyph Single Enum
PointSizeSingleEnum.gen <- setGlyphEnum("PointSize", 
  levels = c("1", "2", "5", "10"), contains = "GlyphEnum")
obj <- new("PointSizeSingleEnum", "1")
obj

## ----------------------------------------------------------------------
##                   change levels
## ----------------------------------------------------------------------

geomSingleEnum <- setSingleEnum("geom", c("rect", "triangle"))
obj <- geomSingleEnum("rect")

## change levels
levels(obj)
levels(obj) <- c("rect", "circle")

## changed levels must include current value
try(levels(obj) <- c("triangle", "circle"))

## ----------------------------------------------------------------------
##                   change levels
## ----------------------------------------------------------------------
obj <- factor("a", levels = letters)
SingleEnum(obj)
MultipleEnum(obj)

objectProperties documentation built on May 3, 2022, 1:08 a.m.