Getting a vector into a function that expects a vector<Base*>

Question

Consider these classes.

class Base
{
   ...
};

class Derived : public Base
{
   ...
};

this function

void BaseFoo( std::ve         


        

Answer 1

If std::vector supported what you're asking for, then it would be possible to defeat the C++ type system without using any casts (edit: ChrisN's link to the C++ FAQ Lite talks about the same issue):

class Base {};
class Derived1 : public Base {};
class Derived2 : public Base {};

void pushStuff(std::vector& vec) {
    vec.push_back(new Derived2);
    vec.push_back(new Base);
}

...
std::vector vec;
pushStuff(vec); // Not legal
// Now vec contains a Derived2 and a Base!

Since your BaseFoo() function takes the vector by value, it cannot modify the original vector that you passed in, so what I wrote would not be possible. But if it takes a non-const reference and you use reinterpret_cast&>() to pass your std::vector, you might not get the result that you want, and your program might crash.

Java arrays support covariant subtyping, and this requires Java to do a runtime type check every time you store a value in an array. This too is undesirable.