C++ :: Encapsulating Speed Types Of Different Animals

#include <iostream>
#define show(variable) std::cout << #variable << " = " << variable << std::endl;
class LivingBeing {
protected:
struct Speed {

[Code] ....

Though the above works, memory is being wasted for speed types that do not pertain to many animals (a snail only crawls, a human never flies, etc...). Saving and loading their files will involve a lot of useless zeros. The problem seems simple, but I can't think of a good redesign to encapsulate speed properly for each of the many, many types of animals. Note that main() works with speed from the base class LivingBeing.

Should there be polymorphic Speed types within each Animal subtype? Then there will be a lot of identical Speed subtypes (e.g. many animals can only swim).

Something like:

class AnimalsThatOnlySwimOrCrawl : LivingBeing {
protected:
struct Speed : LivingBeing::Speed {
int swimmingSpeed, crawlingSpeed;
virtual void increase() override {swimmingSpeed *= 2; crawlingSpeed *= 2;}

[Code] .....