solidity/libsolutil/Visitor.h

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/*
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
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/**
* Visitor templates.
*/
#pragma once
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namespace solidity::util
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{
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/**
* 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.
*
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* Fallback with no return (it will not fail if you do not specify all variants):
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* std::visit(GenericVisitor{
* VisitorFallback<>{},
* [](Class1& _c) { _c.f(); },
* [](Class2& _c) { _c.g(); }
* }, variant);
*
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* Fallback with return type R (the fallback returns `R{}`:
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* std::visit(GenericVisitor{
* VisitorFallback<R>{},
* [](Class1& _c) { _c.f(); },
* [](Class2& _c) { _c.g(); }
* }, variant);
*/
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template <typename...> struct VisitorFallback;
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template <typename R>
struct VisitorFallback<R> { template<typename T> R operator()(T&&) const { return {}; } };
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template<>
struct VisitorFallback<> { template<typename T> void operator()(T&&) const {} };
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template <typename... Visitors> struct GenericVisitor: Visitors... { using Visitors::operator()...; };
template <typename... Visitors> GenericVisitor(Visitors...) -> GenericVisitor<Visitors...>;
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}