This function has an input validation step. If the input vector is not numeric, then it will give a message as "The input must be numeric". The validation part has been defined as follows:

      if(!is.numeric(numVec))
        stop("The input must be numeric")

Once the validation step passes, the function internally calculates everything for summary statistics, such as mean, standard deviation, median, and MAD. In the next step, the S4 class definition has been introduced as follows:

    descriptiveStats <- setClass("descriptiveStats",  
    slots=list(centre="numeric", spread="numeric"))

Now, based on the value of the type argument in the function, it returns either classical or robust descriptive statistics and the return object will have the S4 class descriptiveStats.