template<class ForwardIterator, class T>
constexpr void fill(ForwardIterator first, ForwardIterator last, const T& value);
template<class ExecutionPolicy, class ForwardIterator, class T>
void fill(ExecutionPolicy&& exec,
ForwardIterator first, ForwardIterator last, const T& value);
template<class OutputIterator, class Size, class T>
constexpr OutputIterator fill_n(OutputIterator first, Size n, const T& value);
template<class ExecutionPolicy, class ForwardIterator, class Size, class T>
ForwardIterator fill_n(ExecutionPolicy&& exec,
ForwardIterator first, Size n, const T& value);