mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
87 lines
2.3 KiB
C++
87 lines
2.3 KiB
C++
/*
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This file is part of solidity.
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solidity is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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solidity is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with solidity. If not, see <http://www.gnu.org/licenses/>.
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*/
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#pragma once
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#include <libsolutil/Assertions.h>
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#include <libsolutil/Exceptions.h>
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#include <memory>
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#include <optional>
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#include <utility>
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namespace solidity::util
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{
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DEV_SIMPLE_EXCEPTION(BadSetOnceReassignment);
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DEV_SIMPLE_EXCEPTION(BadSetOnceAccess);
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/// A class that stores a value that can only be set once
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/// \tparam T the type of the stored value
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template<typename T>
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class SetOnce
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{
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public:
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/// Initializes the class to have no stored value.
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SetOnce() = default;
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// Not copiable
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SetOnce(SetOnce const&) = delete;
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SetOnce(SetOnce&&) = delete;
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// Not movable
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SetOnce& operator=(SetOnce const&) = delete;
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SetOnce& operator=(SetOnce&&) = delete;
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/// @brief Sets the stored value to \p _newValue
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/// @throws BadSetOnceReassignment when the stored value has already been set
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/// @return `*this`
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constexpr SetOnce& operator=(T _newValue) &
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{
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assertThrow(
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!m_value.has_value(),
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BadSetOnceReassignment,
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"Attempt to reassign to a SetOnce that already has a value."
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);
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m_value.emplace(std::move(_newValue));
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return *this;
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}
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/// @return A reference to the stored value. The returned reference has the same lifetime as `*this`.
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/// @throws BadSetOnceAccess when the stored value has not yet been set
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T const& operator*() const
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{
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assertThrow(
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m_value.has_value(),
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BadSetOnceAccess,
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"Attempt to access the value of a SetOnce that does not have a value."
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);
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return m_value.value();
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}
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/// @return A reference to the stored value. The referent of the returned pointer has the same lifetime as `*this`.
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/// @throws BadSetOnceAccess when the stored value has not yet been set
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T const* operator->() const { return std::addressof(**this); }
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private:
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std::optional<T> m_value = std::nullopt;
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};
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}
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