How to remove constness of const_iterator?

There is a solution with constant time complexity in C++11: for any sequence, associative, or unordered associative container (including all of the Standard Library containers), you can call the range-erase member function with an empty range:

template <typename Container, typename ConstIterator>
typename Container::iterator remove_constness(Container& c, ConstIterator it)
    return c.erase(it, it);

The range-erase member functions have a pair of const_iterator parameters, but they return an iterator. Because an empty range is provided, the call to erase does not change the contents of the container.

Hat tip to Howard Hinnant and Jon Kalb for this trick.

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