/src/solidity/libsolutil/SetOnce.h

Source
/*
  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;
};

}

Coverage Report

Created: 2025-09-04 07:34