match.enum.arg: Add support for defining another default value than only the first one

[aryoda]

e. g. add a new parameter...

DISADVANTAGE: The default value cannot be recognized in the function signature but only in the documentation!

Is there any chance for a solution that also makes the default value visible in the function signature?

[aryoda]

Implementation idea:

Specify default value via an expression in the function declaration:

f <- function(x = EnumWithDefault(color.enum, color.enum$BLUE) {
  x.value <- match.enum.arg(x, color.enum, color.enum$BLUE)
...
 return(x.value)
}

match.enum.arg must always be called with both arguments then to still support all enum values as allowed values. A 3rd argument is required then to pass in the default value.

Any idea to simplify this even more?