Re: Future of C++
On Aug 21, 5:01 pm, Bart van Ingen Schenau <b...@ingen.ddns.info>
wrote:
Alex wrote:
On Aug 10, 2:02 am, Bart van Ingen Schenau <b...@ingen.ddns.info>
wrote:
Why all the complication, when you can simply do
typeid(*pb); /* where pb is a pointer to the base class */
The standard guarantees that this yields the type_info for the most
derived class, if the base class is polymorphic.
True, however if the parent class has no virtual functions, it doesn't
happen. Inheritance is not synonym for polymorphism. A design may call
for just extending the base interface in derived classes. Or
inheriting only the behavior from the base class.
That said, try this and see what you get:
#include <iostream>
class Base {};
class Derived : public Base {};
int main()
{
Derived* pd = new Derived;
Base* pb = pd;
std::cout << typeid(*pb).name() << std::endl;
delete pd;
}
MSVC and gcc will print the base type name. I'd say that any compliant
compiler should do the same.
They should, just like in this example:
#include <iostream>
#include <typeinfo>
class Base
{
std::type_info& get_type() const
{
return typeid(*this);
}};
class Derived : public Base
{
std::type_info& get_type() const
{
return typeid(*this);
}};
int main()
{
Derived* pd = new Derived;
Base* pb = pd;
std::cout << pb->get_type().name() << std::endl;
delete pd;
}
I fail to see your point. My main point was that version with virtual
get_type() will behave as one would expect (return typeid of the
Derived when called through pointer to base), while non-virtual would
not.
When the parent class has virtual functions, I suspect the performance
penalty of typeid(*pb) will be the same as for dynamic_cast and
virtual call returning typeid(*this) may be a cheaper way to go.
Based on how I would implement RTTI for polymorphic classes, I don't
share your assessment.
<snip>
You may be as well right there, I have just speculated. Again, my
point was that the original statement about laughing at the code
snippet (allegedly from Ogre) with virtual function returning typeid
was condescending and not at all justified. The example can be a valid
approach in some circumstances.
Alex
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