match.enum.arg: Match the passed enum value against the list of allowed enum...

In aryoda/R_enumerations: Adds an enumeration data type for R to support list of allowed value/label pairs

Description

Call this function at the beginning of your own function that uses an enum parameter to validate the passed enum value against the list of allowed enum values.

Usage

match.enum.arg(arg, choices)

Arguments

arg	The actual function parameter that shall be validated against the allowed enum values
choices	Optional: The list of allowed enum values. You can omit this parameter if the formal parameter is declared via name = EnumVariableName. If you provide the enum variable name via an expression you have to specify this parameter to avoid errors when checking for the allowed values.

Details

You can pass an enum value name or the value itself.

If no enum value is passed (missing parameter value) the first item of the enum is used as default value.

Based on the R code of the base function match.arg.

Inspired by https://stackoverflow.com/questions/33838392/enum-like-arguments-in-r

Value

Returns the passed actual parameter if is a valid enum value. If no actual parameter was passed it returns the first element of the enum.

Examples

ColorEnum <- list(BLUE = 1L, RED = 2L, BLACK = 3L)

print_color_code = function(enum = ColorEnum) { 
  i <- match.enum.arg(enum)
  print(i)
  invisible(i)
}

print_color_code(ColorEnum$RED) # use a value from the enum (with auto completion support)
# [1] 2
print_color_code()              # takes the first color of the ColorEnum
# [1] 1
print_color_code(3)             # an integer enum value (dirty, just for demonstration)
# [1] 3
## Not run: 
print_color_code(4)             # an invalid number
# Error in match.enum.arg(enum) : 
#  'arg' must be one of the values in the 'choices' list: BLUE = 1, RED = 2, BLACK = 3

## End(Not run)


PAYMENT_FREQUENCY <- create.enum(c(12, 4, 1), c("MONTHLY", "QUARTERLY", "ANNUALY"))

payment.amount <- function(annual.amount, payment.frequency = PAYMENT_FREQUENCY) {
  payments.per.year <- match.enum.arg(payment.frequency)
  return(annual.amount / payments.per.year)
}

payment.amount(120, PAYMENT_FREQUENCY$MONTHLY)
# [1] 10
payment.amount(120, PAYMENT_FREQUENCY$QUARTERLY)
# [1] 30
## Not run: 
payment.amount(120, 2)
# Error in match.enum.arg(payment.frequency) : 
#  'arg' must be one of the values in the 'choices' list: MONTHLY = 12, QUARTERLY = 4, ANNUALY = 1 

## End(Not run)

payment.amount(120)   # uses the first value as default value!
# [1] 10

aryoda/R_enumerations documentation built on Dec. 9, 2019, 8:51 a.m.