Example of problem:
struct GenericService {
virtual bool DoOtherThing() const = 0;
void DoComplexThing() {
...
bool doOtherThing = DoOtherThing();
if (doOtherThing) { ... }
...
}
};
struct SpecificService : GenericService {
bool DoOtherThingToo() const override final { return true; }
};
Issues:
- It's a violation of the zero-overhead rule that I have to call a virtual function just to get a polymorphic constant.
- No formal way to specify if DoOtherThing() should always return the same value.
Proposed solution:
struct GenericService {
virtual bool const vc_doOtherThing = 0;
void DoComplexThing() {
...
if (vc_doOtherThing) { ... }
...
}
}
struct SpecificService : GenericService {
bool const vc_doOtherThing override final { true };
};
Instead of storing a function pointer in the virtual table, and then calling the function pointer to get a value; it should be possible to just store the value in the virtual table.
This should work for plain-old-data types with trivial construction and destruction. There's no desperate need to support virtual std::string members or std::vectors, which would involve significant complications. Storing plain-old-data types is not complex, though.
denis