solidity/libsolutil/SetOnce.h
2020-09-22 17:38:21 +02:00

89 lines
2.4 KiB
C++

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