std::ranges::generate - cppreference.com (original) (raw)

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.

Contents

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

[edit] Parameters

[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 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 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 #include #include #include #include   auto dice() { static std::uniform_int_distribution 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