solidity/libsolutil/LazyInit.h

96 lines
2.7 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/>.
*/
// SPDX-License-Identifier: GPL-3.0
#pragma once
#include <libsolutil/Assertions.h>
#include <libsolutil/Exceptions.h>
#include <memory>
#include <optional>
#include <type_traits>
#include <utility>
namespace solidity::util
{
DEV_SIMPLE_EXCEPTION(BadLazyInitAccess);
/**
* A value that is initialized at some point after construction of the LazyInit. The stored value can only be accessed
* while calling "init", which initializes the stored value (if it has not already been initialized).
*
* @tparam T the type of the stored value; may not be a function, reference, array, or void type; may be const-qualified.
*/
template<typename T>
class LazyInit
{
public:
using value_type = T;
static_assert(std::is_object_v<value_type>, "Function, reference, and void types are not supported");
static_assert(!std::is_array_v<value_type>, "Array types are not supported.");
static_assert(!std::is_volatile_v<value_type>, "Volatile-qualified types are not supported.");
LazyInit() = default;
LazyInit(LazyInit const&) = delete;
LazyInit& operator=(LazyInit const&) = delete;
// Move constructor must be overridden to ensure that moved-from object is left empty.
constexpr LazyInit(LazyInit&& _other) noexcept:
m_value(std::move(_other.m_value))
{
_other.m_value.reset();
}
LazyInit& operator=(LazyInit&& _other) noexcept
{
this->m_value.swap(_other.m_value);
_other.m_value.reset();
}
template<typename F>
value_type& init(F&& _fun)
{
doInit(std::forward<F>(_fun));
return m_value.value();
}
template<typename F>
value_type const& init(F&& _fun) const
{
doInit(std::forward<F>(_fun));
return m_value.value();
}
private:
/// Although not quite logically const, this is marked const for pragmatic reasons. It doesn't change the platonic
/// value of the object (which is something that is initialized to some computed value on first use).
template<typename F>
void doInit(F&& _fun) const
{
if (!m_value.has_value())
m_value.emplace(std::forward<F>(_fun)());
}
mutable std::optional<value_type> m_value;
};
}