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generator.hpp
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258 lines (204 loc) · 5.64 KB
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///////////////////////////////////////////////////////////////////////////////
// Copyright (c) Lewis Baker
// Licenced under MIT license. See LICENSE.txt for details.
///////////////////////////////////////////////////////////////////////////////
#ifndef CPPCORO_GENERATOR_HPP_INCLUDED
#define CPPCORO_GENERATOR_HPP_INCLUDED
#include <experimental/coroutine>
#include <type_traits>
#include <utility>
#include <exception>
namespace cppcoro
{
template<typename T>
class generator;
namespace detail
{
template<typename T>
class generator_promise
{
public:
using value_type = std::remove_reference_t<T>;
using reference_type = std::conditional_t<std::is_reference_v<T>, T, T&>;
using pointer_type = value_type*;
generator_promise() = default;
generator<T> get_return_object() noexcept;
constexpr std::experimental::suspend_always initial_suspend() const { return {}; }
constexpr std::experimental::suspend_always final_suspend() const { return {}; }
template<
typename U = T,
std::enable_if_t<!std::is_rvalue_reference<U>::value, int> = 0>
std::experimental::suspend_always yield_value(std::remove_reference_t<T>& value) noexcept
{
m_value = std::addressof(value);
return {};
}
std::experimental::suspend_always yield_value(std::remove_reference_t<T>&& value) noexcept
{
m_value = std::addressof(value);
return {};
}
void unhandled_exception()
{
m_exception = std::current_exception();
}
void return_void()
{
}
reference_type value() const noexcept
{
return static_cast<reference_type>(*m_value);
}
// Don't allow any use of 'co_await' inside the generator coroutine.
template<typename U>
std::experimental::suspend_never await_transform(U&& value) = delete;
void rethrow_if_exception()
{
if (m_exception)
{
std::rethrow_exception(m_exception);
}
}
private:
pointer_type m_value;
std::exception_ptr m_exception;
};
struct generator_sentinel {};
template<typename T>
class generator_iterator
{
using coroutine_handle = std::experimental::coroutine_handle<generator_promise<T>>;
public:
using iterator_category = std::input_iterator_tag;
// What type should we use for counting elements of a potentially infinite sequence?
using difference_type = std::size_t;
using value_type = typename generator_promise<T>::value_type;
using reference = typename generator_promise<T>::reference_type;
using pointer = typename generator_promise<T>::pointer_type;
// Iterator needs to be default-constructible to satisfy the Range concept.
generator_iterator() noexcept
: m_coroutine(nullptr)
{}
explicit generator_iterator(coroutine_handle coroutine) noexcept
: m_coroutine(coroutine)
{}
bool operator==(const generator_iterator& other) const noexcept
{
return m_coroutine == other.m_coroutine;
}
bool operator==(generator_sentinel) const noexcept
{
return !m_coroutine || m_coroutine.done();
}
bool operator!=(const generator_iterator& other) const noexcept
{
return !(*this == other);
}
bool operator!=(generator_sentinel other) const noexcept
{
return !operator==(other);
}
generator_iterator& operator++()
{
m_coroutine.resume();
if (m_coroutine.done())
{
m_coroutine.promise().rethrow_if_exception();
}
return *this;
}
// Need to provide post-increment operator to implement the 'Range' concept.
void operator++(int)
{
(void)operator++();
}
reference operator*() const noexcept
{
return m_coroutine.promise().value();
}
pointer operator->() const noexcept
{
return std::addressof(operator*());
}
private:
coroutine_handle m_coroutine;
};
}
template<typename T>
class [[nodiscard]] generator
{
public:
using promise_type = detail::generator_promise<T>;
using iterator = detail::generator_iterator<T>;
generator() noexcept
: m_coroutine(nullptr)
{}
generator(generator&& other) noexcept
: m_coroutine(other.m_coroutine)
{
other.m_coroutine = nullptr;
}
generator(const generator& other) = delete;
~generator()
{
if (m_coroutine)
{
m_coroutine.destroy();
}
}
generator& operator=(generator other) noexcept
{
swap(other);
return *this;
}
iterator begin()
{
if (m_coroutine)
{
m_coroutine.resume();
if (m_coroutine.done())
{
m_coroutine.promise().rethrow_if_exception();
}
}
return iterator{ m_coroutine };
}
detail::generator_sentinel end() noexcept
{
return detail::generator_sentinel{};
}
void swap(generator& other) noexcept
{
std::swap(m_coroutine, other.m_coroutine);
}
private:
friend class detail::generator_promise<T>;
explicit generator(std::experimental::coroutine_handle<promise_type> coroutine) noexcept
: m_coroutine(coroutine)
{}
std::experimental::coroutine_handle<promise_type> m_coroutine;
};
template<typename T>
void swap(generator<T>& a, generator<T>& b)
{
a.swap(b);
}
namespace detail
{
template<typename T>
generator<T> generator_promise<T>::get_return_object() noexcept
{
using coroutine_handle = std::experimental::coroutine_handle<generator_promise<T>>;
return generator<T>{ coroutine_handle::from_promise(*this) };
}
}
template<typename FUNC, typename T>
generator<std::invoke_result_t<FUNC&, typename generator<T>::iterator::reference>> fmap(FUNC func, generator<T> source)
{
for (auto&& value : source)
{
co_yield std::invoke(func, static_cast<decltype(value)>(value));
}
}
}
#endif