passing a polymorphic vectors

Question

I have an polymorphic problem.

void func(std::vector< BaseClass* > A){}

std::vector< SubClass* > B;

func(B); //Compile error C2664 

I get an error like so:

 error C2664 'func' : cannot convert parameter from 'std::vector<_Ty>' to 'std::vector<_Ty>' with
[
    _Ty=B *
]
and
[
    _Ty=A *
]

I also tried some weird stuff like have the parameter be a pointer to the vector and I pass the address of the vector like so:

void func(std::vector< BaseClass* > *A){}

std::vector< SubClass* > B;
func(&B); //same error  

Answer 1

There is no such thing as a polymorphic vector. An std::vector, and every other container type in C++, including C style arrays always contains exactly one type. And the fact that two different containers have types that are related doesn't make the types of the containers related in any way.

In your case, you'll probably have to construct a second vector:

func( std::vector< BaseClass* >( B.begin(), B.end() ) );

Note that trying to use an std::vector<DerivedClass*> as an std::vector<BaseClass*>, say by using a reinterpret_cast, is undefined behavior, and may not work. There's no guarantee that the actual phyical address of the BaseClass subobject in a DerivedClass object have the same pysical address as the complete object.

Answer 2

Templates to the rescue:

template<typename T>
void func(std::vector<T> A)
{
    ...
}