Re: Is this class design correct? A better way?

"Alf P. Steinbach" <>
Sat, 17 Feb 2007 00:01:03 +0100
* nw:

I was wondering if someone would be able to give me some comments on
the following class structure, it feels to me as if there must be a
better way, but I'm unsure what it is, perhaps I should be using
multiple inheritance?

You should be using /inheritance/ and-or /templating/ instead of a type

For inheritance, you can represent the integration algorithm directly as
a derived class override of a Body virtual member function, or you can
represent it as an object passed to the Body constructor(s).


Compilable example code implementing this design follows. Apologies if
I've been overly verbose.

Any help greatly appreciated!


#include <iostream>

Formally you also need <ostream>.

using namespace std;

class Body {

  double x, y, z;
  double a;

Public member variables = ungood.

Name 'a' = ungood.

  static const int BODY_INTEGRATE_EULER=1;
  static const int BODY_INTEGRATE_VERLET=2;
  static const int BODY_INTEGRATE_LEAPFROG=3;

All uppercase for non-macros = ungood.

  int integration_type;

'int' to represent something with limited number of possible values =

Representing type as value = in general, and in this case, ungood.

  virtual bool calculate_force(Body &b) = 0;

  Body() {

See the FAQ item titled 'Should my constructors use "initialization
lists" or "assignment"?', currently available at <url:>.

  bool integrate() {
    if(integration_type == BODY_INTEGRATE_EULER) {
      // .. do euler
      cout << "Euler integration" << endl;
      return true;
    } else
    if(integration_type == BODY_INTEGRATE_VERLET) {
      // .. do verlet
      cout << "Verlet integration" << endl;
      return true;
    } else
    if(integration_type == BODY_INTEGRATE_LEAPFROG) {
      // .. do leapfrog
      cout << "Leapfrog integration" << endl;
      return true;

This type selection is what you need to avoid.

A: Because it messes up the order in which people normally read text.
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A: Top-posting.
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