Why is a vector of pointers not castable to a const vector of const pointers?

Question

The type vector is not convertible to const vector. For example, the following gives a compilation error:

Answer 1

In general, C++ does not allow you to cast someclass to someclass as a template someclass might be specialized for U. It doesn't matter how T and U are related. This mean that the implementation and thus the object layout might be different.

Sadly, there is no way to tell the compiler in which cases the layout and/or behaviour didn't change and the cast should be accepted. I imagine it could be very useful for std::shared_ptr and other use-cases, but that is not going to happen anytime soon (AFAIK).