From:

"roy axenov" <r_axenov@mail.ru>

Newsgroups:

comp.lang.c++

Date:

23 Feb 2007 13:52:09 -0800

Message-ID:

<1172267528.739040.185670@k78g2000cwa.googlegroups.com>

On Feb 23, 10:36 pm, tbring...@gmail.com wrote:

I am interested in a way of having a class call a general

member function of another class.

Specifically, I am trying to write an ordinary

differential equation class that would solve a general

equation in the form: dx/dt = f(x,t).

member function of another class.

Specifically, I am trying to write an ordinary

differential equation class that would solve a general

equation in the form: dx/dt = f(x,t).

I believe you're making a conceptual mistake here. In the

design you're describing f(x,t) is not represented by a

method of a class, but by the class itself, and f a (x,t) -

by an instance of the class representing f(x,t) functions.

That's why you probably shouldn't try passing a pointer to

a method, pass a reference to the object instead. If you

have more general questions about all of this, you probably

should follow-up to comp.object.

The ode class shouldn't know anything about f, except how

to call it.

to call it.

That's pretty much a textbook description of an interface.

[...]

a member of the ode solver, but then I would have to

write a new ode solver for every new class of functions

to be used for f or to have all these derive from some

kind of base class, which I would prefer to avoid.

write a new ode solver for every new class of functions

to be used for f or to have all these derive from some

kind of base class, which I would prefer to avoid.

That kinda defeats the purpose of OOD, doesn't it?

My question is: is there a simple and elegant way to do

this? I would think that similar issues have been

encountered many times before.

this? I would think that similar issues have been

encountered many times before.

I'm not sure if this will work for you, but consider this

bare-bones implementation:

#include <iostream>

class interface_function

{

public :

virtual double operator ( )

( double x , double t ) const = 0 ;

} ;

class ode

{

public :

static void solve ( const interface_function & f ) ;

} ;

void ode :: solve ( const interface_function & f )

{

std :: cout <<

f

(

static_cast < double > ( 1 ) ,

static_cast < double > ( 1 )

) ;

std :: cout << std :: endl ;

}

class f : public interface_function

{

public :

double a_ ;

f ( ) : a_ ( 1 ) { }

virtual double operator ( )

( double x , double t ) const ;

} ;

double f :: operator ( )

( double x , double t ) const

{

return t + x * a_ ;

}

class g : public interface_function

{

public :

double a_ ;

g ( ) : a_ ( 1 ) { }

virtual double operator ( )

( double x , double t ) const ;

} ;

double g :: operator ( )

( double x , double t ) const

{

return t - x * a_ ;

}

int main ( )

{

f f1 ;

g g1 ;

ode :: solve ( f1 ) ;

ode :: solve ( g1 ) ;

f1 . a_ = 5 ;

g1 . a_ = 5 ;

ode :: solve ( f1 ) ;

ode :: solve ( g1 ) ;

}

--

roy axenov

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