How in Mathematica, would I define a function that takes arguments much like one would in an object orientated language

Question

I would know how to write a function in object orientated language, just I don't know how to do this in mathematica, in an OOP I would define a function like this:

int rss = null;

 int Define_RSS(int a, int b, int c, int d){

  int output = (code functionality)
  rss = (some more functionality)
  return output
}

I would like to know how to do the equivalent in mathematica.

Answer 1

rss = None;

DefineRSS[a_, b_, c_, d_] := Module[
        {output=(* code functionality *)},
        rss = (* some more functionality *);
        output
    ]

First we initialize the variable rss to None. Then we define (using SetDelayed) a function DefineRSS (Note we can't use _ because Mathematica will interpret that as a pattern). We use Module to define a temporary variable, set rss, and then evaluate the temporary variable.

Note that if you need more than one line to define output (e.g., you define it iteratively in multiple operations) you can use this form:

DefineRSS[a_, b_, c_, d_] := Module[{output},
        output=(* code functionality *);
        output=(* even more functionality *);
        rss = (* some more functionality *);
        output
    ]