std::ranges::generate
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Feature test macros (C++20)
Concepts library (C++20)
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Algorithm library
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
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Constrained algorithms
All names in this menu belong to namespace
std::ranges
(C++23)
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(C++23)
Defined in header
<algorithm>
Call signature
template< std::input_or_output_iterator O, std::sentinel_for <O> S,
(1)
(since C++20)
std::copy_constructible F >
requires std::invocable <F&> && std::indirectly_writable <O, std::invoke_result_t <F&>>
constexpr O
template< class R, std::copy_constructible F >
(2)
(since C++20)
requires std::invocable <F&> && ranges::output_range <R, std::invoke_result_t <F&>>
constexpr ranges::borrowed_iterator_t <R>
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 algorithm function objects (informally known as niebloids), that is:
- Explicit template argument lists cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.
[edit] Parameters
first, last
-
the iterator-sentinel pair defining the range of elements to modify
r
-
the range of elements to modify
gen
-
the generator function object
[edit] Return value
An output iterator that compares equal to last.
[edit] Complexity
Exactly ranges::distance (first, last) invocations of gen() and assignments.
[edit] 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 {};
[edit] 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& r, int init) { std::ranges::generate(r, [init] mutable { return init++; }); } 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
[edit] See also
(C++26)
(algorithm function object)[edit]