vector and const

Question

Consider this

 void f(vector& p)
 {
 }
 int main()
 { 
  vector nonConstVec;
  f(nonConstVec);
 }

The followi

Answer 1

Templates are a bit strange that way. The fact that there's an implicit conversion from T to U doesn't mean that there's an implicit conversion from XXX to XXX. It can be made to happen, but it takes a fair amount of extra work in the template code to make it happen, and offhand, I doubt the techniques were all known when std::vector was being designed (more accurately, I'm pretty sure they weren't known).

Edit: Issues like this are part of the motivation behind using iterators. Even though a container of X isn't implicitly convertible to a container of const X, a container::iterator is implicitly convertible to a container::const_iterator.

If you replace your:

void f(vector& p) {}

with:

template 
void f(const_iter b, const_iter e) {}

Then:

int main() { 
    vector nonConstVec;
    f(nonConstVec.begin(), nonConstVec.end());
    return 0;
}

will be just fine -- and so will:

vector constVec;
f(constVec.begin(), constVec.end());