| Permutation operations |
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| Operations on uninitialized storage |
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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;
...
[edit] Parameters
first, last
-
the iterator-sentinel pair defining the
range of elements to fill with sequentially increasing values starting with
value
value
-
initial value to store; the expression ++value must be well-formed
[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 <O> 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 <R>, 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;
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 <algorithm>
#include <functional>
#include <iostream>
#include <list>
#include <numeric>
#include <random>
#include <vector>
template <typename Proj = std::identity >
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 <int> 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 <int>::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
copy-assigns the given value to every element in a range
(function template) [edit]
assigns a range of elements a certain value
(algorithm function object)[edit]
assigns the results of successive function calls to every element in a range
(function template) [edit]
saves the result of a function in a range
(algorithm function object)[edit]
a
view consisting of a sequence generated by repeatedly incrementing an initial value
(class template) (customization point object)[edit]
fills a range with successive increments of the starting value
(function template) [edit]