solidity/libsolutil/Visitor.h
2022-04-26 01:52:56 +02:00

73 lines
2.3 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
/**
* Visitor templates.
*/
#pragma once
namespace solidity::util
{
/**
* Generic visitor used as follows:
* std::visit(GenericVisitor{
* [](Class1& _c) { _c.f(); },
* [](Class2& _c) { _c.g(); }
* }, variant);
* This one does not have a fallback and will fail at
* compile-time if you do not specify all variants.
*
* Fallback with no return (it will not fail if you do not specify all variants):
* std::visit(GenericVisitor{
* VisitorFallback<>{},
* [](Class1& _c) { _c.f(); },
* [](Class2& _c) { _c.g(); }
* }, variant);
*
* Fallback with return type R (the fallback returns `R{}`:
* std::visit(GenericVisitor{
* VisitorFallback<R>{},
* [](Class1& _c) { _c.f(); },
* [](Class2& _c) { _c.g(); }
* }, variant);
*/
template <typename...> struct VisitorFallback;
template <typename R>
struct VisitorFallback<R> { template<typename T> R operator()(T&&) const { return {}; } };
template<>
struct VisitorFallback<> { template<typename T> void operator()(T&&) const {} };
// MSVC. Empty base class optimization does not happen in some scenarios.
// Enforcing it with __declspec(empty_bases) avoids MSVC Debug test crash
// (Run-Time Check Failure #2 - Stack around the variable '....' was corrupted).
// See https://docs.microsoft.com/en-us/cpp/cpp/empty-bases,
// https://developercommunity.visualstudio.com/t/10005513.
#if defined(_MSC_VER)
#define SOLC_EMPTY_BASES __declspec(empty_bases)
#else
#define SOLC_EMPTY_BASES
#endif
template <typename... Visitors> struct SOLC_EMPTY_BASES GenericVisitor: Visitors... { using Visitors::operator()...; };
template <typename... Visitors> GenericVisitor(Visitors...) -> GenericVisitor<Visitors...>;
}