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// generator - Single-header, ranges-compatible generator type built
// on C++20 coroutines
// Written in 2021 by Sy Brand (tartanllama@gmail.com, @TartanLlama)
//
// Documentation available at https://tl.tartanllama.xyz/
//
// To the extent possible under law, the author(s) have dedicated all
// copyright and related and neighboring rights to this software to the
// public domain worldwide. This software is distributed without any warranty.
//
// You should have received a copy of the CC0 Public Domain Dedication
// along with this software. If not, see
// <http://creativecommons.org/publicdomain/zero/1.0/>.
export module nihil.core:generator;
import nihil.std;
namespace nihil {
export template <typename T>
struct generator
{
private:
struct promise
{
using value_type = std::remove_reference_t<T>;
using reference_type =
std::conditional_t<std::is_pointer_v<value_type>, value_type, value_type &>;
using pointer_type =
std::conditional_t<std::is_pointer_v<value_type>, value_type, value_type *>;
promise() = default;
[[nodiscard]] auto get_return_object() -> generator
{
return generator(std::coroutine_handle<promise>::from_promise(*this));
}
[[nodiscard]] auto initial_suspend() const -> std::suspend_always
{
return {};
}
[[nodiscard]] auto final_suspend() const noexcept -> std::suspend_always
{
return {};
}
void return_void() const noexcept
{
}
void unhandled_exception() noexcept
{
exception_ = std::current_exception();
}
void rethrow_if_exception()
{
if (exception_) {
std::rethrow_exception(exception_);
}
}
std::suspend_always yield_value(value_type &&v) noexcept
{
value_ = std::move(v);
return {};
}
std::suspend_always yield_value(value_type const &v) noexcept
requires(!std::is_reference_v<T>)
{
value_ = v;
return {};
}
std::suspend_always yield_value(value_type &v) noexcept
requires(std::is_reference_v<T>)
{
value_ = &v;
return {};
}
std::exception_ptr exception_;
std::variant<std::monostate, value_type, value_type *> value_;
};
public:
using promise_type = promise;
class sentinel
{
};
class iterator
{
using handle_type = std::coroutine_handle<promise_type>;
public:
using value_type = typename promise_type::value_type;
using reference_type = typename promise_type::reference_type;
using pointer_type = typename promise_type::pointer_type;
using difference_type = std::ptrdiff_t;
iterator() = default;
~iterator()
{
if (handle_)
handle_.destroy();
}
// Non-copyable because coroutine handles point to a unique resource
iterator(iterator const &) = delete;
iterator(iterator &&rhs) noexcept
: handle_(std::exchange(rhs.handle_, nullptr))
{
}
auto operator=(iterator const &) -> iterator & = delete;
auto operator=(iterator &&rhs) noexcept -> iterator &
{
handle_ = std::exchange(rhs.handle_, nullptr);
return *this;
}
friend auto operator==(iterator const &it, sentinel) noexcept -> bool
{
return (!it.handle_ || it.handle_.done());
}
auto operator++() -> iterator &
{
handle_.resume();
if (handle_.done()) {
handle_.promise().rethrow_if_exception();
}
return *this;
}
void operator++(int)
{
(void)this->operator++();
}
reference_type operator*() const
noexcept(noexcept(std::is_nothrow_copy_constructible_v<reference_type>))
requires(std::is_reference_v<T>)
{
return *std::get<value_type *>(handle_.promise().value_);
}
reference_type operator*() const
noexcept(noexcept(std::is_nothrow_copy_constructible_v<reference_type>))
requires(!std::is_reference_v<T>)
{
return std::get<value_type>(handle_.promise().value_);
}
value_type *operator->() const
noexcept(noexcept(std::is_nothrow_copy_constructible_v<reference_type>))
requires(std::is_reference_v<T>)
{
return std::get<value_type *>(handle_.promise().value_);
}
value_type *operator->() const
noexcept(noexcept(std::is_nothrow_copy_constructible_v<reference_type>))
requires(!std::is_reference_v<T>)
{
return &std::get<value_type>(handle_.promise().value_);
}
private:
friend struct generator;
explicit iterator(handle_type handle)
: handle_(handle)
{
}
handle_type handle_;
};
using handle_type = std::coroutine_handle<promise_type>;
generator() noexcept = default;
~generator()
{
if (handle_)
handle_.destroy();
}
generator(generator const &) = delete;
generator(generator &&rhs) noexcept
: handle_(std::exchange(rhs.handle_, nullptr))
{
}
auto operator=(generator const &) -> generator & = delete;
auto operator=(generator &&rhs) noexcept -> generator &
{
swap(rhs);
return *this;
}
auto begin() -> iterator
{
handle_.resume();
if (handle_.done()) {
handle_.promise().rethrow_if_exception();
}
return iterator(std::exchange(handle_, nullptr));
}
auto end() const noexcept -> sentinel
{
return {};
}
void swap(generator &other) noexcept
{
std::swap(handle_, other.handle_);
}
private:
friend class iterator;
explicit generator(handle_type handle) noexcept
: handle_(handle)
{
}
handle_type handle_ = nullptr;
};
} // namespace nihil
export template <typename T>
inline constexpr bool std::ranges::enable_view<nihil::generator<T>> = true;
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