mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
95 lines
2.6 KiB
C++
95 lines
2.6 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 <type_traits>
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#include <utility>
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namespace solidity::util
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{
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DEV_SIMPLE_EXCEPTION(BadLazyInitAccess);
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/**
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* A value that is initialized at some point after construction of the LazyInit. The stored value can only be accessed
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* while calling "init", which initializes the stored value (if it has not already been initialized).
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*
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* @tparam T the type of the stored value; may not be a function, reference, array, or void type; may be const-qualified.
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*/
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template<typename T>
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class LazyInit
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{
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public:
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using value_type = T;
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static_assert(std::is_object_v<value_type>, "Function, reference, and void types are not supported");
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static_assert(!std::is_array_v<value_type>, "Array types are not supported.");
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static_assert(!std::is_volatile_v<value_type>, "Volatile-qualified types are not supported.");
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LazyInit() = default;
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LazyInit(LazyInit const&) = delete;
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LazyInit& operator=(LazyInit const&) = delete;
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// Move constructor must be overridden to ensure that moved-from object is left empty.
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constexpr LazyInit(LazyInit&& _other) noexcept:
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m_value(std::move(_other.m_value))
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{
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_other.m_value.reset();
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}
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LazyInit& operator=(LazyInit&& _other) noexcept
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{
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this->m_value.swap(_other.m_value);
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_other.m_value.reset();
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}
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template<typename F>
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value_type& init(F&& _fun)
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{
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doInit(std::forward<F>(_fun));
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return m_value.value();
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}
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template<typename F>
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value_type const& init(F&& _fun) const
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{
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doInit(std::forward<F>(_fun));
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return m_value.value();
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}
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private:
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/// Although not quite logically const, this is marked const for pragmatic reasons. It doesn't change the platonic
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/// value of the object (which is something that is initialized to some computed value on first use).
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template<typename F>
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void doInit(F&& _fun) const
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{
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if (!m_value.has_value())
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m_value.emplace(std::forward<F>(_fun)());
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}
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mutable std::optional<value_type> m_value;
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};
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}
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