auto it = vector.begin() resulting type is not convertible to const_iterator

Question

Containers are required to provide an iterator type which is implicitly convertible to a const_iterator. Given this, I am trying to use auto

Answer 1

The problem has nothing common with the iterator conversion. The compiler simply unable to determine the template argument. It is the same if you would write

int x = 10;
long y = 20;

std::cout << std::max( x, y ) << std::endl;

though an object of type int can be implicitly converted to an object of type long.

As for your example you could write

const size_t n = std::distance::const_iterator> (it, itr);