Re: How make polymorphism optional?

From:

tony_in_da_uk@yahoo.co.uk

Newsgroups:

comp.lang.c++

Date:

Tue, 9 Sep 2008 07:28:32 -0700 (PDT)

Message-ID:

<1ec625f9-4641-4a3a-8c5e-853bf586d5a2@b38g2000prf.googlegroups.com>

On Sep 9, 1:49 pm, tony_in_da...@yahoo.co.uk wrote:

On Sep 7, 11:35 am, tony_in_da...@yahoo.co.uk wrote:

On Sep 7, 12:09 am, Litvinov Sergey <slitvi...@gmail.com> wrote:

Sometime I have no objects of Derived class and in those cases
I would like to get rid of polymorphism overhead. (speed is crucial
for
me). It is OK for me to have
a separate binary to handle those cases. But the only design I came u=

with is
with preprocessor to "separate" virtual keyword in class definition

class Base {
#ifdefine NOPOLYMORPHISM
void
method();
#else
virtual void
method();
#endif

}

and the part of the program where the concrete type of the objects is
defined should
be also modified.

Is there any better way to do that?

Perhaps something like:

struct Base
{
  virtual void virtual_method() { base_method(); }
  void base_method();
  void method() { if (s_use_virtual_) virtual_method(); else
base_method(); }
  static bool s_use_virtual_;

};

And set s_use_virtual_ at runtime based on whether you've created any
derived objects. It still has some run-time overhead, but I think
you'll find it's pretty small compared to out-of-line function
invocation.

Actually, a faster option is to create a concrete class with the Base
class's content, then a non-virtual inline function to access that
content. You can put your code that operates on all the loaded data
into a template function, and depending on whether you've seen a
derived object call either the instantiation for the virtual-dispatch
version or that for the concrete classes.

Tony

One more thing: even if you do have a derived object, you can
explicitly force a call to the base class implementation using p-

Base::method();

Tony