Let's give a name to the function that you are going to write here, desStat, and define its action as follows:

    desStat <- function(numVec, type="classical"){
      if(!is.numeric(numVec))
       stop("The input must be numeric")
      average <- mean(numVec, na.rm = T)
      std <- sd(numVec, na.rm = T)
      med <- median(numVec, na.rm = T)
      mad <- mad(numVec, na.rm = T)
      descriptiveStats <- setClass("descriptiveStats",   
      slots=list(centre="numeric",    
      spread="numeric"))
      if(type=="classical")
        return(new("descriptiveStats", centre=average, spread=std))
          if(type=="robust")
             return(new("descriptiveStats", centre=med, spread=mad))
        }
 
    desStat(x)
    An object of class "descriptiveStats"
    Slot "centre":
    [1] 19.8

    Slot "spread":
    [1] 5.256677