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Add ripple::Expected which simulates std::expected:
Also integrates use of ripple::Expected into the code base.
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| Original file line number | Diff line number | Diff line change |
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| //------------------------------------------------------------------------------ | ||
| /* | ||
| This file is part of rippled: https://github.com/ripple/rippled | ||
| Copyright (c) 2021 Ripple Labs Inc. | ||
| Permission to use, copy, modify, and/or distribute this software for any | ||
| purpose with or without fee is hereby granted, provided that the above | ||
| copyright notice and this permission notice appear in all copies. | ||
| THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES | ||
| WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF | ||
| MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR | ||
| ANY SPECIAL , DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES | ||
| WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN | ||
| ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF | ||
| OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. | ||
| */ | ||
| //============================================================================== | ||
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| #ifndef RIPPLE_BASICS_EXPECTED_H_INCLUDED | ||
| #define RIPPLE_BASICS_EXPECTED_H_INCLUDED | ||
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| #include <ripple/basics/contract.h> | ||
| #include <boost/outcome.hpp> | ||
| #include <stdexcept> | ||
| #include <type_traits> | ||
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| namespace ripple { | ||
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| /** Expected is an approximation of std::expected (hoped for in C++23) | ||
| See: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p0323r10.html | ||
| The implementation is entirely based on boost::outcome_v2::result. | ||
| */ | ||
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| // Exception thrown by an invalid access to Expected. | ||
| struct bad_expected_access : public std::runtime_error | ||
| { | ||
| bad_expected_access() : runtime_error("bad expected access") | ||
| { | ||
| } | ||
| }; | ||
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| namespace detail { | ||
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| // Custom policy for Expected. Always throw on an invalid access. | ||
| struct throw_policy : public boost::outcome_v2::policy::base | ||
| { | ||
| template <class Impl> | ||
| static constexpr void | ||
| wide_value_check(Impl&& self) | ||
| { | ||
| if (!base::_has_value(std::forward<Impl>(self))) | ||
| Throw<bad_expected_access>(); | ||
| } | ||
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| template <class Impl> | ||
| static constexpr void | ||
| wide_error_check(Impl&& self) | ||
| { | ||
| if (!base::_has_error(std::forward<Impl>(self))) | ||
| Throw<bad_expected_access>(); | ||
| } | ||
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| template <class Impl> | ||
| static constexpr void | ||
| wide_exception_check(Impl&& self) | ||
| { | ||
| if (!base::_has_exception(std::forward<Impl>(self))) | ||
| Throw<bad_expected_access>(); | ||
| } | ||
| }; | ||
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| } // namespace detail | ||
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| // Definition of Unexpected, which is used to construct the unexpected | ||
| // return type of an Expected. | ||
| template <class E> | ||
| class Unexpected | ||
| { | ||
| public: | ||
| static_assert(!std::is_same<E, void>::value, "E must not be void"); | ||
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| Unexpected() = delete; | ||
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| constexpr explicit Unexpected(E const& e) : val_(e) | ||
| { | ||
| } | ||
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| constexpr explicit Unexpected(E&& e) : val_(std::move(e)) | ||
| { | ||
| } | ||
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| constexpr const E& | ||
| value() const& | ||
| { | ||
| return val_; | ||
| } | ||
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| constexpr E& | ||
| value() & | ||
| { | ||
| return val_; | ||
| } | ||
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| constexpr E&& | ||
| value() && | ||
| { | ||
| return std::move(val_); | ||
| } | ||
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| constexpr const E&& | ||
| value() const&& | ||
| { | ||
| return std::move(val_); | ||
| } | ||
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| private: | ||
| E val_; | ||
| }; | ||
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| // Unexpected deduction guide that converts array to const*. | ||
| template <typename E, std::size_t N> | ||
| Unexpected(E (&)[N]) -> Unexpected<E const*>; | ||
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| // Definition of Expected. All of the machinery comes from boost::result. | ||
| template <class T, class E> | ||
| class [[nodiscard]] Expected | ||
| : private boost::outcome_v2::result<T, E, detail::throw_policy> | ||
| { | ||
| using Base = boost::outcome_v2::result<T, E, detail::throw_policy>; | ||
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| public: | ||
| template < | ||
| typename U, | ||
| typename = std::enable_if_t<std::is_convertible_v<U, T>>> | ||
| constexpr Expected(U r) : Base(T{std::forward<U>(r)}) | ||
| { | ||
| } | ||
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| template < | ||
| typename U, | ||
| typename = std::enable_if_t<std::is_convertible_v<U, E>>> | ||
| constexpr Expected(Unexpected<U> e) : Base(E{std::forward<U>(e.value())}) | ||
| { | ||
| } | ||
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| constexpr bool has_value() const | ||
| { | ||
| return Base::has_value(); | ||
| } | ||
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| constexpr T const& value() const | ||
| { | ||
| return Base::value(); | ||
| } | ||
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| constexpr T& value() | ||
| { | ||
| return Base::value(); | ||
| } | ||
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| constexpr E const& error() const | ||
| { | ||
| return Base::error(); | ||
| } | ||
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| constexpr E& error() | ||
| { | ||
| return Base::error(); | ||
| } | ||
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| constexpr explicit operator bool() const | ||
| { | ||
| return has_value(); | ||
| } | ||
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| // Add operator* and operator-> so the Expected API looks a bit more like | ||
| // what std::expected is likely to look like. See: | ||
| // http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p0323r10.html | ||
| [[nodiscard]] constexpr T& operator*() | ||
| { | ||
| return this->value(); | ||
| } | ||
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| [[nodiscard]] constexpr T const& operator*() const | ||
| { | ||
| return this->value(); | ||
| } | ||
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| [[nodiscard]] constexpr T* operator->() | ||
| { | ||
| return &this->value(); | ||
| } | ||
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| [[nodiscard]] constexpr T const* operator->() const | ||
| { | ||
| return &this->value(); | ||
| } | ||
| }; | ||
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| // Specialization of Expected<void, E>. Allows returning either success | ||
| // (without a value) or the reason for the failure. | ||
| template <class E> | ||
| class [[nodiscard]] Expected<void, E> | ||
| : private boost::outcome_v2::result<void, E, detail::throw_policy> | ||
| { | ||
| using Base = boost::outcome_v2::result<void, E, detail::throw_policy>; | ||
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| public: | ||
| // The default constructor makes a successful Expected<void, E>. | ||
| // This aligns with std::expected behavior proposed in P0323R10. | ||
| constexpr Expected() : Base(boost::outcome_v2::success()) | ||
| { | ||
| } | ||
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| template < | ||
| typename U, | ||
| typename = std::enable_if_t<std::is_convertible_v<U, E>>> | ||
| constexpr Expected(Unexpected<U> e) : Base(E{std::forward<U>(e.value())}) | ||
| { | ||
| } | ||
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| constexpr E const& error() const | ||
| { | ||
| return Base::error(); | ||
| } | ||
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| constexpr E& error() | ||
| { | ||
| return Base::error(); | ||
| } | ||
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| constexpr explicit operator bool() const | ||
| { | ||
| return Base::has_value(); | ||
| } | ||
| }; | ||
|
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| } // namespace ripple | ||
|
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| #endif // RIPPLE_BASICS_EXPECTED_H_INCLUDED |
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