+++ /dev/null
-/*
- * Copyright 2017 Facebook, Inc.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-#pragma once
-
-#include <functional>
-#include <iterator>
-#include <memory>
-#include <tuple>
-#include <type_traits>
-#include <utility>
-
-#include <folly/Functional.h>
-
-namespace folly {
-
-/**
- * Argument tuple for variadic emplace/constructor calls. Stores arguments by
- * (decayed) value. Restores original argument types with reference qualifiers
- * and adornments at unpack time to emulate perfect forwarding.
- *
- * Uses inheritance instead of a type alias to std::tuple so that emplace
- * iterators with implicit unpacking disabled can distinguish between
- * emplace_args and std::tuple parameters.
- *
- * @seealso folly::make_emplace_args
- * @seealso folly::get_emplace_arg
- */
-template <typename... Args>
-struct emplace_args : public std::tuple<std::decay_t<Args>...> {
- using storage_type = std::tuple<std::decay_t<Args>...>;
- using storage_type::storage_type;
-};
-
-/**
- * Pack arguments in a tuple for assignment to a folly::emplace_iterator,
- * folly::front_emplace_iterator, or folly::back_emplace_iterator. The
- * iterator's operator= will unpack the tuple and pass the unpacked arguments
- * to the container's emplace function, which in turn forwards the arguments to
- * the (multi-argument) constructor of the target class.
- *
- * Argument tuples generated with folly::make_emplace_args will be unpacked
- * before being passed to the container's emplace function, even for iterators
- * where implicit_unpack is set to false (so they will not implicitly unpack
- * std::pair or std::tuple arguments to operator=).
- *
- * Arguments are copied (lvalues) or moved (rvalues). To avoid copies and moves,
- * wrap references using std::ref(), std::cref(), and folly::rref(). Beware of
- * dangling references, especially references to temporary objects created with
- * folly::rref().
- *
- * Note that an argument pack created with folly::make_emplace_args is different
- * from an argument pack created with std::make_pair or std::make_tuple.
- * Specifically, passing a std::pair&& or std::tuple&& to an emplace iterator's
- * operator= will pass rvalue references to all fields of that tuple to the
- * container's emplace function, while passing an emplace_args&& to operator=
- * will cast those field references to the exact argument types as passed to
- * folly::make_emplace_args previously. If all arguments have been wrapped by
- * std::reference_wrappers or folly::rvalue_reference_wrappers, the result will
- * be the same as if the container's emplace function had been called directly
- * (perfect forwarding), with no temporary copies of the arguments.
- *
- * @seealso folly::rref
- *
- * @example
- * class Widget { Widget(int, int); };
- * std::vector<Widget> makeWidgets(const std::vector<int>& in) {
- * std::vector<Widget> out;
- * std::transform(
- * in.begin(),
- * in.end(),
- * folly::back_emplacer(out),
- * [](int i) { return folly::make_emplace_args(i, i); });
- * return out;
- * }
- */
-template <typename... Args>
-emplace_args<Args...> make_emplace_args(Args&&... args) noexcept(
- noexcept(emplace_args<Args...>(std::forward<Args>(args)...))) {
- return emplace_args<Args...>(std::forward<Args>(args)...);
-}
-
-namespace detail {
-template <typename Arg>
-decltype(auto) unwrap_emplace_arg(Arg&& arg) noexcept {
- return std::forward<Arg>(arg);
-}
-template <typename Arg>
-decltype(auto) unwrap_emplace_arg(std::reference_wrapper<Arg> arg) noexcept {
- return arg.get();
-}
-template <typename Arg>
-decltype(auto) unwrap_emplace_arg(
- folly::rvalue_reference_wrapper<Arg> arg) noexcept {
- return std::move(arg).get();
-}
-}
-
-/**
- * Getter function for unpacking a single emplace argument.
- *
- * Calling get_emplace_arg on an emplace_args rvalue reference results in
- * perfect forwarding of the original input types. A special case are
- * std::reference_wrapper and folly::rvalue_reference_wrapper objects within
- * folly::emplace_args. These are also unwrapped so that the bare reference is
- * returned.
- *
- * std::get is not a customization point in the standard library, so the
- * cleanest solution was to define our own getter function.
- */
-template <size_t I, typename... Args>
-decltype(auto) get_emplace_arg(emplace_args<Args...>&& args) noexcept {
- using Out = std::tuple<Args...>;
- return detail::unwrap_emplace_arg(
- std::forward<std::tuple_element_t<I, Out>>(std::get<I>(args)));
-}
-template <size_t I, typename... Args>
-decltype(auto) get_emplace_arg(emplace_args<Args...>& args) noexcept {
- return detail::unwrap_emplace_arg(std::get<I>(args));
-}
-template <size_t I, typename... Args>
-decltype(auto) get_emplace_arg(const emplace_args<Args...>& args) noexcept {
- return detail::unwrap_emplace_arg(std::get<I>(args));
-}
-template <size_t I, typename Args>
-decltype(auto) get_emplace_arg(Args&& args) noexcept {
- return std::get<I>(std::move(args));
-}
-template <size_t I, typename Args>
-decltype(auto) get_emplace_arg(Args& args) noexcept {
- return std::get<I>(args);
-}
-template <size_t I, typename Args>
-decltype(auto) get_emplace_arg(const Args& args) noexcept {
- return std::get<I>(args);
-}
-
-namespace detail {
-/**
- * Emplace implementation class for folly::emplace_iterator.
- */
-template <typename Container>
-struct Emplace {
- Emplace(Container& c, typename Container::iterator i)
- : container(std::addressof(c)), iter(std::move(i)) {}
- template <typename... Args>
- void emplace(Args&&... args) {
- iter = container->emplace(iter, std::forward<Args>(args)...);
- ++iter;
- }
- Container* container;
- typename Container::iterator iter;
-};
-
-/**
- * Emplace implementation class for folly::hint_emplace_iterator.
- */
-template <typename Container>
-struct EmplaceHint {
- EmplaceHint(Container& c, typename Container::iterator i)
- : container(std::addressof(c)), iter(std::move(i)) {}
- template <typename... Args>
- void emplace(Args&&... args) {
- iter = container->emplace_hint(iter, std::forward<Args>(args)...);
- ++iter;
- }
- Container* container;
- typename Container::iterator iter;
-};
-
-/**
- * Emplace implementation class for folly::front_emplace_iterator.
- */
-template <typename Container>
-struct EmplaceFront {
- explicit EmplaceFront(Container& c) : container(std::addressof(c)) {}
- template <typename... Args>
- void emplace(Args&&... args) {
- container->emplace_front(std::forward<Args>(args)...);
- }
- Container* container;
-};
-
-/**
- * Emplace implementation class for folly::back_emplace_iterator.
- */
-template <typename Container>
-struct EmplaceBack {
- explicit EmplaceBack(Container& c) : container(std::addressof(c)) {}
- template <typename... Args>
- void emplace(Args&&... args) {
- container->emplace_back(std::forward<Args>(args)...);
- }
- Container* container;
-};
-
-/**
- * Generic base class and implementation of all emplace iterator classes.
- *
- * Uses the curiously recurring template pattern (CRTP) to cast `this*` to
- * `Derived*`; i.e., to implement covariant return types in a generic manner.
- */
-template <typename Derived, typename EmplaceImpl, bool implicit_unpack>
-class emplace_iterator_base;
-
-/**
- * Partial specialization of emplace_iterator_base with implicit unpacking
- * disabled.
- */
-template <typename Derived, typename EmplaceImpl>
-class emplace_iterator_base<Derived, EmplaceImpl, false>
- : protected EmplaceImpl /* protected implementation inheritance */ {
- public:
- // Iterator traits.
- using iterator_category = std::output_iterator_tag;
- using value_type = void;
- using difference_type = void;
- using pointer = void;
- using reference = void;
- using container_type =
- std::remove_reference_t<decltype(*EmplaceImpl::container)>;
-
- using EmplaceImpl::EmplaceImpl;
-
- /**
- * Canonical output operator. Forwards single argument straight to container's
- * emplace function.
- */
- template <typename T>
- Derived& operator=(T&& arg) {
- this->emplace(std::forward<T>(arg));
- return static_cast<Derived&>(*this);
- }
-
- /**
- * Special output operator for packed arguments. Unpacks args and performs
- * variadic call to container's emplace function.
- */
- template <typename... Args>
- Derived& operator=(emplace_args<Args...>& args) {
- return unpackAndEmplace(args, std::index_sequence_for<Args...>{});
- }
- template <typename... Args>
- Derived& operator=(const emplace_args<Args...>& args) {
- return unpackAndEmplace(args, std::index_sequence_for<Args...>{});
- }
- template <typename... Args>
- Derived& operator=(emplace_args<Args...>&& args) {
- return unpackAndEmplace(
- std::move(args), std::index_sequence_for<Args...>{});
- }
-
- // No-ops.
- Derived& operator*() {
- return static_cast<Derived&>(*this);
- }
- Derived& operator++() {
- return static_cast<Derived&>(*this);
- }
- Derived& operator++(int) {
- return static_cast<Derived&>(*this);
- }
-
- // We need all of these explicit defaults because the custom operator=
- // overloads disable implicit generation of these functions.
- emplace_iterator_base(const emplace_iterator_base&) = default;
- emplace_iterator_base(emplace_iterator_base&&) noexcept = default;
- emplace_iterator_base& operator=(emplace_iterator_base&) = default;
- emplace_iterator_base& operator=(const emplace_iterator_base&) = default;
- emplace_iterator_base& operator=(emplace_iterator_base&&) noexcept = default;
-
- protected:
- template <typename Args, std::size_t... I>
- Derived& unpackAndEmplace(Args& args, std::index_sequence<I...>) {
- this->emplace(get_emplace_arg<I>(args)...);
- return static_cast<Derived&>(*this);
- }
- template <typename Args, std::size_t... I>
- Derived& unpackAndEmplace(const Args& args, std::index_sequence<I...>) {
- this->emplace(get_emplace_arg<I>(args)...);
- return static_cast<Derived&>(*this);
- }
- template <typename Args, std::size_t... I>
- Derived& unpackAndEmplace(Args&& args, std::index_sequence<I...>) {
- this->emplace(get_emplace_arg<I>(std::move(args))...);
- return static_cast<Derived&>(*this);
- }
-};
-
-/**
- * Partial specialization of emplace_iterator_base with implicit unpacking
- * enabled.
- *
- * Uses inheritance rather than SFINAE. operator= requires a single argument,
- * which makes it very tricky to use std::enable_if or similar.
- */
-template <typename Derived, typename EmplaceImpl>
-class emplace_iterator_base<Derived, EmplaceImpl, true>
- : public emplace_iterator_base<Derived, EmplaceImpl, false> {
- private:
- using Base = emplace_iterator_base<Derived, EmplaceImpl, false>;
-
- public:
- using Base::Base;
- using Base::operator=;
-
- /**
- * Special output operator for arguments packed into a std::pair. Unpacks
- * the pair and performs variadic call to container's emplace function.
- */
- template <typename... Args>
- Derived& operator=(std::pair<Args...>& args) {
- return this->unpackAndEmplace(args, std::index_sequence_for<Args...>{});
- }
- template <typename... Args>
- Derived& operator=(const std::pair<Args...>& args) {
- return this->unpackAndEmplace(args, std::index_sequence_for<Args...>{});
- }
- template <typename... Args>
- Derived& operator=(std::pair<Args...>&& args) {
- return this->unpackAndEmplace(
- std::move(args), std::index_sequence_for<Args...>{});
- }
-
- /**
- * Special output operator for arguments packed into a std::tuple. Unpacks
- * the tuple and performs variadic call to container's emplace function.
- */
- template <typename... Args>
- Derived& operator=(std::tuple<Args...>& args) {
- return this->unpackAndEmplace(args, std::index_sequence_for<Args...>{});
- }
- template <typename... Args>
- Derived& operator=(const std::tuple<Args...>& args) {
- return this->unpackAndEmplace(args, std::index_sequence_for<Args...>{});
- }
- template <typename... Args>
- Derived& operator=(std::tuple<Args...>&& args) {
- return this->unpackAndEmplace(
- std::move(args), std::index_sequence_for<Args...>{});
- }
-
- // We need all of these explicit defaults because the custom operator=
- // overloads disable implicit generation of these functions.
- emplace_iterator_base(const emplace_iterator_base&) = default;
- emplace_iterator_base(emplace_iterator_base&&) noexcept = default;
- emplace_iterator_base& operator=(emplace_iterator_base&) = default;
- emplace_iterator_base& operator=(const emplace_iterator_base&) = default;
- emplace_iterator_base& operator=(emplace_iterator_base&&) noexcept = default;
-};
-
-/**
- * Concrete instantiation of emplace_iterator_base. All emplace iterator
- * classes; folly::emplace_iterator, folly::hint_emplace_iterator,
- * folly::front_emplace_iterator, and folly::back_emplace_iterator; are just
- * type aliases of this class.
- *
- * It is not possible to alias emplace_iterator_base directly, because type
- * aliases cannot be used for CRTP.
- */
-template <
- template <typename> class EmplaceImplT,
- typename Container,
- bool implicit_unpack>
-class emplace_iterator_impl
- : public emplace_iterator_base<
- emplace_iterator_impl<EmplaceImplT, Container, implicit_unpack>,
- EmplaceImplT<Container>,
- implicit_unpack> {
- private:
- using Base = emplace_iterator_base<
- emplace_iterator_impl,
- EmplaceImplT<Container>,
- implicit_unpack>;
-
- public:
- using Base::Base;
- using Base::operator=;
-
- // We need all of these explicit defaults because the custom operator=
- // overloads disable implicit generation of these functions.
- emplace_iterator_impl(const emplace_iterator_impl&) = default;
- emplace_iterator_impl(emplace_iterator_impl&&) noexcept = default;
- emplace_iterator_impl& operator=(emplace_iterator_impl&) = default;
- emplace_iterator_impl& operator=(const emplace_iterator_impl&) = default;
- emplace_iterator_impl& operator=(emplace_iterator_impl&&) noexcept = default;
-};
-} // namespace detail
-
-/**
- * Behaves just like std::insert_iterator except that it calls emplace()
- * instead of insert(). Uses perfect forwarding.
- */
-template <typename Container, bool implicit_unpack = true>
-using emplace_iterator =
- detail::emplace_iterator_impl<detail::Emplace, Container, implicit_unpack>;
-
-/**
- * Behaves just like std::insert_iterator except that it calls emplace_hint()
- * instead of insert(). Uses perfect forwarding.
- */
-template <typename Container, bool implicit_unpack = true>
-using hint_emplace_iterator = detail::
- emplace_iterator_impl<detail::EmplaceHint, Container, implicit_unpack>;
-
-/**
- * Behaves just like std::front_insert_iterator except that it calls
- * emplace_front() instead of insert(). Uses perfect forwarding.
- */
-template <typename Container, bool implicit_unpack = true>
-using front_emplace_iterator = detail::
- emplace_iterator_impl<detail::EmplaceFront, Container, implicit_unpack>;
-
-/**
- * Behaves just like std::back_insert_iterator except that it calls
- * emplace_back() instead of insert(). Uses perfect forwarding.
- */
-template <typename Container, bool implicit_unpack = true>
-using back_emplace_iterator = detail::
- emplace_iterator_impl<detail::EmplaceBack, Container, implicit_unpack>;
-
-/**
- * Convenience function to construct a folly::emplace_iterator, analogous to
- * std::inserter().
- *
- * Setting implicit_unpack to false will disable implicit unpacking of
- * single std::pair and std::tuple arguments to the iterator's operator=. That
- * may be desirable in case of constructors that expect a std::pair or
- * std::tuple argument.
- */
-template <bool implicit_unpack = true, typename Container>
-emplace_iterator<Container, implicit_unpack> emplacer(
- Container& c,
- typename Container::iterator i) {
- return emplace_iterator<Container, implicit_unpack>(c, std::move(i));
-}
-
-/**
- * Convenience function to construct a folly::hint_emplace_iterator, analogous
- * to std::inserter().
- *
- * Setting implicit_unpack to false will disable implicit unpacking of
- * single std::pair and std::tuple arguments to the iterator's operator=. That
- * may be desirable in case of constructors that expect a std::pair or
- * std::tuple argument.
- */
-template <bool implicit_unpack = true, typename Container>
-hint_emplace_iterator<Container, implicit_unpack> hint_emplacer(
- Container& c,
- typename Container::iterator i) {
- return hint_emplace_iterator<Container, implicit_unpack>(c, std::move(i));
-}
-
-/**
- * Convenience function to construct a folly::front_emplace_iterator, analogous
- * to std::front_inserter().
- *
- * Setting implicit_unpack to false will disable implicit unpacking of
- * single std::pair and std::tuple arguments to the iterator's operator=. That
- * may be desirable in case of constructors that expect a std::pair or
- * std::tuple argument.
- */
-template <bool implicit_unpack = true, typename Container>
-front_emplace_iterator<Container, implicit_unpack> front_emplacer(
- Container& c) {
- return front_emplace_iterator<Container, implicit_unpack>(c);
-}
-
-/**
- * Convenience function to construct a folly::back_emplace_iterator, analogous
- * to std::back_inserter().
- *
- * Setting implicit_unpack to false will disable implicit unpacking of
- * single std::pair and std::tuple arguments to the iterator's operator=. That
- * may be desirable in case of constructors that expect a std::pair or
- * std::tuple argument.
- */
-template <bool implicit_unpack = true, typename Container>
-back_emplace_iterator<Container, implicit_unpack> back_emplacer(Container& c) {
- return back_emplace_iterator<Container, implicit_unpack>(c);
-}
-}
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