Re: private inheritance vs containment
In article <f3erhm$fnq$1@mouse.otenet.gr>, Sam <sakarab@yahoo.com>
wrote:
Seungbeom Kim wrote:
Sam wrote:
... and the (small) extra performance private inheritance
gives is needed.
However, I cannot imagine a case where private inheritance will give
you any extra performance over containment. Can you give an example?
When a contained object member function is called, its "this" pointer
must be calculated and passed to it. On the other hand in an inheritance
relationship the "this" pointer is the same with the derived object. No
calculation needed.
The above is a micro-optimization that the compiler can likely take care
of itself.
Example:
struct A
{
void do_work();
};
// containment
class B
{
private:
A mA;
public:
void do_work() { mA.do_work(); }
}
// private inheritance
class C : private A
{
public:
void do_work() { A::do_work(); }
}
int main()
{
B b;
// gets address of b, calculates address of
// B::mA and calls A::do_work()
b.do_work();
C c;
// gets address of c, directlly calls A::do_work()
c.do_work();
}
In the above code, the B::do_work function would likely be expanded
inline which means the "calculation" you speak of is done at compile
time, not run time. No performance advantage here.
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