std::ranges::generate
From cppreference.com
| Defined in header <algorithm>
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| Call signature |
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| template< std::input_or_output_iterator O, std::sentinel_for<O> S, std::copy_constructible F > |
(1) | (since C++20) |
| template< class R, std::copy_constructible F > requires std::invocable<F&> && ranges::output_range<R, std::invoke_result_t<F&>> |
(2) | (since C++20) |
1) Assigns the result of successive invocations of the function object
gen to each element in the range [first, last).2) Same as (1), but uses
r as the range, as if using ranges::begin(r) as first and ranges::end(r) as last.The function-like entities described on this page are niebloids, that is:
- Explicit template argument lists may not be specified when calling any of them.
- None of them is visible to argument-dependent lookup.
- When one of them is found by normal unqualified lookup for the name to the left of the function-call operator, it inhibits argument-dependent lookup.
In practice, they may be implemented as function objects, or with special compiler extensions.
Parameters
| first, last | - | the range of elements to modify |
| r | - | the range of elements to modify |
| gen | - | the generator function object |
Return value
An output iterator that compares equal to last.
Complexity
Exactly ranges::distance(first, last) invocations of gen() and assignments.
Possible implementation
struct generate_fn { template<std::input_or_output_iterator O, std::sentinel_for<O> S, std::copy_constructible F> requires std::invocable<F&> && std::indirectly_writable<O, std::invoke_result_t<F&>> constexpr O operator()( O first, S last, F gen ) const { for (; first != last; *first = std::invoke(gen), ++first); return first; } template<class R, std::copy_constructible F> requires std::invocable<F&> && ranges::output_range<R, std::invoke_result_t<F&>> constexpr ranges::borrowed_iterator_t<R> operator()( R&& r, F gen ) const { return (*this)(ranges::begin(r), ranges::end(r), std::move(gen)); } }; inline constexpr generate_fn generate{}; |
Example
Run this code
#include <algorithm> #include <array> #include <iostream> #include <random> #include <string_view> auto dice() { static std::uniform_int_distribution<int> distr{1, 6}; static std::random_device device; static std::mt19937 engine{device()}; return distr(engine); } void iota(auto& v, int n) { std::ranges::generate(v, [&n] () mutable { return n++; }); } void print(std::string_view comment, const auto& v) { for (std::cout << comment; int i : v) { std::cout << i << ' '; } std::cout << '\n'; } int main() { std::array<int, 8> v; std::ranges::generate(v.begin(), v.end(), dice); print("dice: ", v); std::ranges::generate(v, dice); print("dice: ", v); iota(v, 1); print("iota: ", v); }
Possible output:
dice: 4 3 1 6 6 4 5 5 dice: 4 2 5 3 6 2 6 2 iota: 1 2 3 4 5 6 7 8
See also
| (C++20) |
saves the result of N applications of a function (niebloid) |
| (C++20) |
assigns a range of elements a certain value (niebloid) |
| (C++20) |
assigns a value to a number of elements (niebloid) |
| (C++20) |
applies a function to a range of elements (niebloid) |
| assigns the results of successive function calls to every element in a range (function template) |