ArgumentCheck (version 0.9.0)

addError: Argument Checking

Description

Checking function arguments can be done in a manner that allows all of the problems in the arguments to be noted and returned to the user in a single call. This avoids the potentially iterative process of finding problems in one argument, fixing the error, and going on to find problems in subsequent checks. The ArgCheck object can store messages for all of the problems and return these messages all at once, allowing the user the opportunity to fix all of the arguments before proceeding.

Usage

addError(expr, msg, argcheck)

addWarning(expr, msg, argcheck)

finishArgCheck(argcheck)

newArgCheck()

Arguments

expr

A logical expression that, when TRUE indicates an error or warning should be returned.

msg

A Character string giving the message to return with an error or warning

argcheck

An object with class ArgCheck, usually created by newArgCheck

Details

newArgCheck initializes an ArgCheck object. This object stores the number of warnings, the number of errors, and the corresponding messages for the warnings and errors. addError and addWarning are used to add messages to the ArgCheck objects. finishArgCheck looks at the ArgCheck object. If it finds any errors or warnings, those are printed for the user to review. When errors are found, the function is terminated.

Examples

#* This example is taken from the discussion of argument checking at
#* http://www.r-bloggers.com/programming-with-r---checking-function-arguments/
cylinder.volume <- function(height, radius){
  ArgCheck <- newArgCheck()
  ArgCheck <- addError(missing(height),
                     "A value for 'height' was not provided",
                     ArgCheck)
  ArgCheck <- addError(ifelse(!missing(height), height < 0, FALSE),
                     "'height' must be a non-negative number",
                     ArgCheck)
  ArgCheck <- addError(missing(radius),
                     "A value for 'radius' was not provided",
                     ArgCheck)
  ArgCheck <- addError(ifelse(!missing(radius), radius < 0, FALSE),
                     "'radius' must be a non-negative number",
                     ArgCheck)

  ArgCheck <- addWarning(ifelse(!missing(height) & !missing(radius),
                              height < radius, FALSE),
                       "When 'height' < 'radius', you have a short, awkward looking cylinder",
                       ArgCheck)

  finishArgCheck(ArgCheck, "cylinder.volume")

  volume <- pi * radius^2 * height
  volume
}

cylinder.volume()
cylinder.volume(height = -3)
cylinder.volume(height = 3, radius = -2)
cylinder.volume(height = 3, radius=2)
cylinder.volume(height = -8, radius = 4)