Hi, I hope this helps in some way. Note: I have no clue what your
problem domain is but I have some indication that the following
sample code will help you in some way. BTW, I did NOT try to compile
the code. I merely wrote it to give you some idea.
Good Luck!
PS. I like to use boost. If you don't, RcPtr can be replaced with
a raw pointer. (www.boost.org)
-------------------------------------------------------------------
#include <boost/shared_ptr.hpp>
class IntegratorImpl
{
public:
typedef boost::shared_ptr<IntegratorImpl> RcPtr;
public:
IntegratorImpl( double a ) : m_a( a ) {}
virtual bool integrate() = 0;
protected:
// I think that a should be here not in Body
// but I don't know what a is.
double m_a;
};
class EulerIntegrator : public IntegratorImpl
{
public:
EulerIntergrator( double a ) : IntegratorImpl( a ) {}
virtual bool integrate()
{
// do Euler integration
}
private:
// put Euler integration specific stuff here
};
// add Vertlet and LeapFrog integrators as separate classes like
// EulerIntegrator
class Integrator
{
public:
enum IntegrateType
{
kNone, kEuler, kVertlet, kLeapFrog
};
public:
Integrator();
~Integrator();
void selectIntegrator( Integrator type, double a )
{
switch( type )
{
case kEuler:
m_impl.reset( new EulerIntegrator( a ));
break;
case kVertlet:
m_impl.reset( new VertletIntegrator( a ));
// you get the idea
default:
// throw? your choice
}
}
bool integrate()
{
if( m_impl )
{
return false;
}
else
{
return m_impl->integrate();
}
}
private:
// just a raw pointer if you do not like boost
IntegratorImpl::RcPtr m_impl;
};
class Body
{
public:
Body();
bool integrate() { return m_integrator.integrate(); }
virtual void selectIntegrator( Integrator::IntegratorType type )
{
// assuming 0 is a good default for a here
m_integrator.selectIntegrator( type, 0 );
}
private:
Integrator m_integrator;
// rest of your data members here
};
class Planet : public Body
{
public:
Planet( const Body &body ) : m_body( body ) {}
double calcForce()
{
// use m_body to calculate a here
double a = 1.0;
return a;
}
virtual void selectIntegrator( Integrator::IntegratorType type )
{
m_integrator.selectIntegrator( type, calcForce() );
}
private:
const Body &m_body;
};
// something similar for SimpleHarmonic
int
main(void)
{
Planet p;
Planet p2;
SimpleHarmonic s;
p.selectIntegrator( Integrator::kLeapFrog );
p2.selectIntegrator( Integrator::kVertlet );
s.selectIntegrator( Integrator::kVertlet );
cout << "planet,leapfrog: ";
p.integrate();
cout << "planet,verlet: ";
p2.integrate();
cout << "simpleharmonic,verlet: ";
s.integrate();
return 0;
}
nw wrote:
Hi,
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?
Basically I have a pure virtual class called Body, this contains a
number of integration algorithms which are applied to the Body.
Generally only one integration algorithm will be used with a
particular Body. The integration algorithm is called by the
integrate() method, which selects the integration algorithm depending
on how you have set the variable integration_type.
I'm not sure if it's relevant to this discussion but Body is the base
class from which two others are derived, these implement the
calculate_force() method, this method updates a variable used by the
integrate() method.
Compilable example code implementing this design follows. Apologies if
I've been overly verbose.
Any help greatly appreciated!
#include <iostream>
using namespace std;
class Body {
public:
double x, y, z;
double a;
static const int BODY_INTEGRATE_EULER=1;
static const int BODY_INTEGRATE_VERLET=2;
static const int BODY_INTEGRATE_LEAPFROG=3;
int integration_type;
virtual bool calculate_force(Body &b) = 0;
Body() {
integration_type=BODY_INTEGRATE_EULER;
}
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;
}
}
};
class Planet : public Body {
virtual bool calculate_force(Body &b) {
// do force calculation for planet... updates a
}
};
class SimpleHarmonic : public Body {
virtual bool calculate_force(Body &b) {
// do force calculation for simple harmonic motion... updates a
}
};
int main(void) {
Planet p;
Planet p2;
SimpleHarmonic s;
p.integration_type = Body::BODY_INTEGRATE_LEAPFROG;
p2.integration_type = Body::BODY_INTEGRATE_VERLET;
s.integration_type = Body::BODY_INTEGRATE_VERLET;
cout << "planet,leapfrog: ";
p.integrate();
cout << "planet,verlet: ";
p2.integrate();
cout << "simpleharmonic,verlet: ";
s.integrate();
return 0;
}
Thank you for both your and Alf P. Steinbach's suggestions.
In my example, a is acceleration. It is a quantity calculated from
of Body. I suppose I could pass the integrator object a reference to
objects, one for each body. Is it possible to avoid this? Are there