std::ranges::generate() algorithm
- od C++20
- Simplified
- Detailed
// (1)
constexpr O generate( O first, S last, F gen );
// (2)
constexpr ranges::borrowed_iterator_t<R> generate( R&& r, F gen );
The type of arguments are generic and have following constraints:
O
-std::input_or_output_iterator
S
-std::sentinel_for<O>
R
- (none)F
-std::copy_constructible
Additionally, each overload has the following constraints:
- (1) -
invocable<F&> && indirectly_writable<O, invoke_result_t<F&>>
- (1) -
invocable<F&> && ranges::output_range<R, invoke_result_t<F&>>
(The std::
namespace was ommitted here for readability)
// (1)
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 generate( O first, S last, F gen );
// (2)
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> generate( R&& r, F gen );
-
(1) Assigns the result of successive invocations of the function object
gen
to each element in the range [first
;last
). -
(2) Same as (2), but uses
r
as the first source range, as if usingranges::begin(r)
asfirst
andranges::end(r)
aslast
.
The function-like entities described on this page are niebloids.
Parameters
first last | The range of the elements to modify. |
r | The range of the 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.
Exceptions
(none)
Possible implementation
generate(1) and generate(2)
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 {};
Examples
#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);
}
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
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