breaking circular dependency?!

[Oliver Kowalke]

Hi,
how could following problem be solved (not the same base class)?

// A.h

class A
{
private:
   const X move_()
   { ... }

public:
   const B f()
   { return B( move_() ); }
};


// B.h

class B
{
private:
   const X move_()
   { ... }

public:
   const A f()
   { return A( move_() ); }
};

 

[Rolf Magnus]

Hi,
how could following problem be solved (not the same base class)?

What base class?

// A.h

class A
{
private:
const X move_()
{ ... }

public:
const B f()
{ return B( move_() ); }
};


// B.h

class B
{
private:
const X move_()
{ ... }

public:
const A f()
{ return A( move_() ); }
};

Don't implement the functions in the header, but in the implementation file.
Then put a forward declaration before the class definition.

 

[zr]

Hi,
how could following problem be solved (not the same base class)?

// A.h

class A
{
private:
   const X move_()
   { ... }

public:
   const B f()
   { return B( move_() ); }

};

// B.h

class B
{
private:
   const X move_()
   { ... }

public:
   const A f()
   { return A( move_() ); }

};

see http://www.parashift.com/c++-faq-lite/misc-technical-issues.html#faq-39..11

 

[Oliver Kowalke]

What base class?

I mean I don't want to have a (shared) base class (as a suggestion)

Don't implement the functions in the header, but in the implementation
file. Then put a forward declaration before the class definition.

forward declarations work for references or pointer in the header - doesn't
the compiler need to know the size of A / B in the header because it A and
B are returned by value and not as refernce or pointer?

 

[Oliver Kowalke]

see
http://www.parashift.com/c++-faq-lite/misc-technical-issues.html#faq-39.11

A and B are returned by value and not as references or pointers.

 

[Rolf Magnus]

forward declarations work for references or pointer in the header -
doesn't the compiler need to know the size of A / B in the header because
it A and B are returned by value and not as refernce or pointer?

No.

 

[Vaclav Haisman]

Oliver Kowalke wrote, On 28.12.2008 18:38:

Hi,
how could following problem be solved (not the same base class)?

// A.h

class A
{
private:
const X move_()
{ ... }

public:
const B f()
{ return B( move_() ); }
};


// B.h

class B
{
private:
const X move_()
{ ... }

public:
const A f()
{ return A( move_() ); }
};

Using forward declaration and moving the methods implementation to place
where the forward declared class is complete. Something like this:


// X.h
struct X
{ };


// A.h
class B;

class A
{
private:
const X move_()
{ return X (); }

public:
A (X = X ())
{ }

const B f();
};


// B.h
class A;

class B
{
private:
const X move_()
{ return X (); }

public:
B (X = X ())
{ }

const A f();
};


// A.cpp
#include "A.h"
#include "B.h"

const B A::f()
{ return B( move_() ); }


// B.cpp
#include "A.h"
#include "B.h"

const A B::f()
{ return A( move_() ); }


// main.cpp
int main ()
{
A a;
B b;

A aa = b.f();
B bb = a.f();
}