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std::ranges::generate

From cppreference.com
< cpp‎ | algorithm‎ | ranges
 
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms: std::ranges::copy, std::ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
(C++11)(C++11)(C++11)
(C++17)
Modifying sequence operations
Operations on uninitialized storage
Partitioning operations
Sorting operations
(C++11)
Binary search operations
Set operations (on sorted ranges)
Heap operations
(C++11)
Minimum/maximum operations
(C++11)
(C++17)

Permutations
Numeric operations
C library
 
Constrained algorithms
Non-modifying sequence operations
Modifying sequence operations
Operations on uninitialized storage
Partitioning operations
Sorting operations
Binary search operations
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations
Permutations
 
Defined in header <algorithm>
Call signature
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 ranges::generate( O first, S last, F gen );
(1) (since C++20)
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>

      ranges::generate( R&& r, F gen );
(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:

In practice, they may be implemented as function objects, or with special compiler extensions.

Contents

[edit] Parameters

first, last - 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

#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

[edit] See also

saves the result of N applications of a function
(niebloid) [edit]
assigns a range of elements a certain value
(niebloid) [edit]
assigns a value to a number of elements
(niebloid) [edit]
applies a function to a range of elements
(niebloid) [edit]
assigns the results of successive function calls to every element in a range
(function template) [edit]