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recursive_generator.hpp
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345 lines (272 loc) · 7.11 KB
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///////////////////////////////////////////////////////////////////////////////
// Copyright (c) Lewis Baker
// Licenced under MIT license. See LICENSE.txt for details.
///////////////////////////////////////////////////////////////////////////////
#ifndef CPPCORO_RECURSIVE_GENERATOR_HPP_INCLUDED
#define CPPCORO_RECURSIVE_GENERATOR_HPP_INCLUDED
#include <cppcoro/generator.hpp>
#include <experimental/coroutine>
#include <type_traits>
#include <utility>
#include <cassert>
#include <functional>
namespace cppcoro
{
template<typename T>
class recursive_generator
{
public:
class promise_type final
{
public:
promise_type() noexcept
: m_value(nullptr)
, m_exception(nullptr)
, m_root(this)
, m_parentOrLeaf(this)
{}
promise_type(const promise_type&) = delete;
promise_type(promise_type&&) = delete;
auto get_return_object() noexcept
{
return recursive_generator<T>{ *this };
}
std::experimental::suspend_always initial_suspend() noexcept
{
return {};
}
std::experimental::suspend_always final_suspend() noexcept
{
return {};
}
void unhandled_exception() noexcept
{
m_exception = std::current_exception();
}
void return_void() noexcept {}
std::experimental::suspend_always yield_value(T& value) noexcept
{
m_value = std::addressof(value);
return {};
}
std::experimental::suspend_always yield_value(T&& value) noexcept
{
m_value = std::addressof(value);
return {};
}
auto yield_value(recursive_generator&& generator) noexcept
{
return yield_value(generator);
}
auto yield_value(recursive_generator& generator) noexcept
{
struct awaitable
{
awaitable(promise_type* childPromise)
: m_childPromise(childPromise)
{}
bool await_ready() noexcept
{
return this->m_childPromise == nullptr;
}
void await_suspend(std::experimental::coroutine_handle<promise_type>) noexcept
{}
void await_resume()
{
if (this->m_childPromise != nullptr)
{
this->m_childPromise->throw_if_exception();
}
}
private:
promise_type* m_childPromise;
};
if (generator.m_promise != nullptr)
{
m_root->m_parentOrLeaf = generator.m_promise;
generator.m_promise->m_root = m_root;
generator.m_promise->m_parentOrLeaf = this;
generator.m_promise->resume();
if (!generator.m_promise->is_complete())
{
return awaitable{ generator.m_promise };
}
m_root->m_parentOrLeaf = this;
}
return awaitable{ nullptr };
}
// Don't allow any use of 'co_await' inside the recursive_generator coroutine.
template<typename U>
std::experimental::suspend_never await_transform(U&& value) = delete;
void destroy() noexcept
{
std::experimental::coroutine_handle<promise_type>::from_promise(*this).destroy();
}
void throw_if_exception()
{
if (m_exception != nullptr)
{
std::rethrow_exception(std::move(m_exception));
}
}
bool is_complete() noexcept
{
return std::experimental::coroutine_handle<promise_type>::from_promise(*this).done();
}
T& value() noexcept
{
assert(this == m_root);
assert(!is_complete());
return *(m_parentOrLeaf->m_value);
}
void pull() noexcept
{
assert(this == m_root);
assert(!m_parentOrLeaf->is_complete());
m_parentOrLeaf->resume();
while (m_parentOrLeaf != this && m_parentOrLeaf->is_complete())
{
m_parentOrLeaf = m_parentOrLeaf->m_parentOrLeaf;
m_parentOrLeaf->resume();
}
}
private:
void resume() noexcept
{
std::experimental::coroutine_handle<promise_type>::from_promise(*this).resume();
}
std::add_pointer_t<T> m_value;
std::exception_ptr m_exception;
promise_type* m_root;
// If this is the promise of the root generator then this field
// is a pointer to the leaf promise.
// For non-root generators this is a pointer to the parent promise.
promise_type* m_parentOrLeaf;
};
recursive_generator() noexcept
: m_promise(nullptr)
{}
recursive_generator(promise_type& promise) noexcept
: m_promise(&promise)
{}
recursive_generator(recursive_generator&& other) noexcept
: m_promise(other.m_promise)
{
other.m_promise = nullptr;
}
recursive_generator(const recursive_generator& other) = delete;
recursive_generator& operator=(const recursive_generator& other) = delete;
~recursive_generator()
{
if (m_promise != nullptr)
{
m_promise->destroy();
}
}
recursive_generator& operator=(recursive_generator&& other) noexcept
{
if (this != &other)
{
if (m_promise != nullptr)
{
m_promise->destroy();
}
m_promise = other.m_promise;
other.m_promise = nullptr;
}
return *this;
}
class iterator
{
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::ptrdiff_t;
using value_type = std::remove_reference_t<T>;
using reference = std::conditional_t<std::is_reference_v<T>, T, T&>;
using pointer = std::add_pointer_t<T>;
iterator() noexcept
: m_promise(nullptr)
{}
explicit iterator(promise_type* promise) noexcept
: m_promise(promise)
{}
bool operator==(const iterator& other) const noexcept
{
return m_promise == other.m_promise;
}
bool operator!=(const iterator& other) const noexcept
{
return m_promise != other.m_promise;
}
iterator& operator++()
{
assert(m_promise != nullptr);
assert(!m_promise->is_complete());
m_promise->pull();
if (m_promise->is_complete())
{
auto* temp = m_promise;
m_promise = nullptr;
temp->throw_if_exception();
}
return *this;
}
void operator++(int)
{
(void)operator++();
}
reference operator*() const noexcept
{
assert(m_promise != nullptr);
return static_cast<reference>(m_promise->value());
}
pointer operator->() const noexcept
{
return std::addressof(operator*());
}
private:
promise_type* m_promise;
};
iterator begin()
{
if (m_promise != nullptr)
{
m_promise->pull();
if (!m_promise->is_complete())
{
return iterator(m_promise);
}
m_promise->throw_if_exception();
}
return iterator(nullptr);
}
iterator end() noexcept
{
return iterator(nullptr);
}
void swap(recursive_generator& other) noexcept
{
std::swap(m_promise, other.m_promise);
}
private:
friend class promise_type;
promise_type* m_promise;
};
template<typename T>
void swap(recursive_generator<T>& a, recursive_generator<T>& b) noexcept
{
a.swap(b);
}
// Note: When applying fmap operator to a recursive_generator we just yield a non-recursive
// generator since we generally won't be using the result in a recursive context.
template<typename FUNC, typename T>
generator<std::invoke_result_t<FUNC&, typename recursive_generator<T>::iterator::reference>> fmap(FUNC func, recursive_generator<T> source)
{
for (auto&& value : source)
{
co_yield std::invoke(func, static_cast<decltype(value)>(value));
}
}
}
#endif