std::ranges::iota, std::ranges::iota_result - cppreference.com (original) (raw)

Fills the range [first, last) with sequentially increasing values, starting with value and repetitively evaluating ++value.

Equivalent operation:

*(first) = value; *(first + 1) = ++value; *(first + 2) = ++value; *(first + 3) = ++value; ...

Contents

• 1 Parameters
• 2 Return value
• 3 Complexity
• 4 Possible implementation
• 5 Notes
• 6 Example
• 7 See also

[edit] Parameters

[edit] Return value

{last, value + ranges::distance(first, last)}

[edit] Complexity

Exactly last - first increments and assignments.

[edit] Possible implementation

struct iota_fn { template<std::input_or_output_iterator O, std::sentinel_for S, std::weakly_incrementable T> requires std::indirectly_writable<O, const T&> constexpr iota_result<O, T> operator()(O first, S last, T value) const { while (first != last) { *first = as_const(value); ++first; ++value; } return {std::move(first), std::move(value)}; }   template<std::weakly_incrementable T, std::ranges::output_range<const T&> R> constexpr iota_result<std::ranges::borrowed_iterator_t, T> operator()(R&& r, T value) const { return (*this)(std::ranges::begin(r), std::ranges::end(r), std::move(value)); } };   inline constexpr iota_fn iota;

[edit] Notes

The function is named after the integer function ⍳ from the programming language APL.

[edit] Example

Uses the vector of iterators (std::vector<std::list<T>::iterator>) as a proxy to shuffle the elements of the std::list, because ranges::shuffle cannot be applied to the std::list directly.

#include #include #include #include #include #include #include   template void println(auto comment, std::ranges::input_range auto&& range, Proj proj = {}) { for (std::cout << comment; auto const &element : range) std::cout << proj(element) << ' '; std::cout << '\n'; }   int main() { std::list list(8);   // Fill the list with ascending values: 0, 1, 2, ..., 7 std::ranges::iota(list, 0); println("List: ", list);   // A vector of iterators (see the comment to Example) std::vector<std::list::iterator> vec(list.size());   // Fill with iterators to consecutive list's elements std::ranges::iota(vec.begin(), vec.end(), list.begin());   std::ranges::shuffle(vec, std::mt19937 {std::random_device {}()}); println("List viewed via vector: ", vec, [](auto it) { return *it; }); }

Possible output:

List: 0 1 2 3 4 5 6 7 List viewed via vector: 5 7 6 0 1 3 4 2

[edit] See also