Re: more inheritance patterns
On Jun 27, 5:39 am, m...@cs.wisc.edu (Mick Charles Beaver) wrote:
At work, someone showed me a way to avoid virtual functions
while maintaining an interface class.
Basically,
class _MyClass {
void Method;
};
#if defined(LINUX)
#include "linux/MyLinuxClass.h"
class MyClass : public MyLinuxClass {};
#elif defined(WINDOWS)
#include "windows/MyWindowsClass.h"
class MyClass : public MyWindowsClass {};
#endif
Then, throughout the code base, MyClass would be used,
following the interface defined in _MyClass, while still
allowing platform-specific code where needed.
My question is, where could I read about more constructions
like this? My coworker called it an "inheritance pattern."
I'd love to learn more about them (even though I'm sure a case
can be made for avoiding this style).
It looks unwieldy and awkward to me. Anytime you need to use
#if's, there's something wrong. The usual solution in such
cases is to define MyClass using the compliation firewall idiom
(so that none of the data members are in the header), and
compile against it. Then provide separate implementations for
each of the platforms, and link against whichever one is
appropriate. Alternatively, the class is an abstract base
class, with all of the functions pure virtual, and a static
function to construct instances; again, you link against the
appropriate library, which contains the definition for the
correct derived class. (In the case of windowing under X,
you'll often defer the linking until runtime, and choose a
dynamically linked object according to some environment variable
or a command line switch, in order to allow the user to choose
whichever look and feel he wants.)
I've called this link time polymorphism once or twice. I
don't know if it has any real generally accepted name, but it's
very wide spread.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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