When might it make sense to use inheritance when templates
(compile-time polymorphism) is enough?
Hello Group!
Prior to templates, if you wanted to reuse code across
different types, you would use inheritance / polymorphism
where your different types would derive from a common
base type that offered the capabilities needed by your
reusable code.
Now (with templates) if you know at compile time which
objects are of which concrete types you can use templates.
(If the concrete type of an object is only determined at
run time, you still need inheritance.)
This is kind of a soft question, but I'm wondering whether
there are situations where inheritance would still be
preferable, even when concrete types are known at compile
time, and a template solution could have been used.
Assume for this question that the code is special purpose,
so we're not trying to write some general, open-ended
library. That is, the code will be reused across a
smallish number of different types that are all being
designed together, and will not be extended to new types
in the future.
Also assume that efficiency isn't a concern, so that we
don't care about the cost of vtables or the cost (size)
of duplicated template code.
To illustrate my question, below is a simple, do-nothing
example that uses both inheritance and templates for
compile-time polymorphism. printPrintable is an
inheritance-based polymorphic function, while
printHasPrintMe is a generic template function.
Thanks for any thoughts and wisdom.
K. Frank
==========
#include <iostream>
class Printable {
public:
virtual void printMePoly() const = 0;
};
class A : public Printable {
public:
void printMePoly() const { std::cout << "aValue_ = " << aValue_ << std::endl; }
int aValue_ = 13;
};
class B {
public:
void printMeGen() const { std::cout << "bValue_ = " << bValue_ << std::endl; }
int bValue_ = 17;
};
void printPrintable (const Printable& p) {
p.printMePoly();
}
template<typename T> void printHasPrintMe (const T& p) {
p.printMeGen();
}
int main (int argc, char *argv[]) {
A a;
B b;
printPrintable (a);
printHasPrintMe (b);
}
==========