path: root/libdevcore/Visitor.h

/*
    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/>.
*/
/**
 * Visitor templates.
 */

#pragma once

#include <functional>
#include <boost/variant/static_visitor.hpp>

namespace dev
{

/// Generic visitor used as follows:
/// boost::apply_visitor(GenericVisitor<Class1, Class2>(
///     [](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.

template <class...>
struct GenericVisitor{};

template <class Visitable, class... Others>
struct GenericVisitor<Visitable, Others...>: public GenericVisitor<Others...>
{
    using GenericVisitor<Others...>::operator ();
    explicit GenericVisitor(
        std::function<void(Visitable&)> _visitor,
        std::function<void(Others&)>... _otherVisitors
    ):
        GenericVisitor<Others...>(std::move(_otherVisitors)...),
        m_visitor(std::move(_visitor))
    {}

    void operator()(Visitable& _v) const { m_visitor(_v); }

    std::function<void(Visitable&)> m_visitor;
};
template <>
struct GenericVisitor<>: public boost::static_visitor<> {
    void operator()() const {}
};

/// Generic visitor with fallback:
/// boost::apply_visitor(GenericFallbackVisitor<Class1, Class2>(
///     [](Class1& _c) { _c.f(); },
///     [](Class2& _c) { _c.g(); }
/// ), variant);
/// This one DOES have a fallback and will NOT fail at
/// compile-time if you do not specify all variants.

template <class...>
struct GenericFallbackVisitor{};

template <class Visitable, class... Others>
struct GenericFallbackVisitor<Visitable, Others...>: public GenericFallbackVisitor<Others...>
{
    explicit GenericFallbackVisitor(
        std::function<void(Visitable&)> _visitor,
        std::function<void(Others&)>... _otherVisitors
    ):
        GenericFallbackVisitor<Others...>(std::move(_otherVisitors)...),
        m_visitor(std::move(_visitor))
    {}

    using GenericFallbackVisitor<Others...>::operator ();
    void operator()(Visitable& _v) const { m_visitor(_v); }

    std::function<void(Visitable&)> m_visitor;
};
template <>
struct GenericFallbackVisitor<>: public boost::static_visitor<> {
    template <class T>
    void operator()(T&) const { }
};

/// Generic visitor with fallback that can return a value:
/// boost::apply_visitor(GenericFallbackReturnsVisitor<ReturnType, Class1, Class2>(
///     [](Class1& _c) { return _c.f(); },
///     [](Class2& _c) { return _c.g(); }
/// ), variant);
/// This one DOES have a fallback and will NOT fail at
/// compile-time if you do not specify all variants.
/// The fallback {}-constructs the return value.

template <class R, class...>
struct GenericFallbackReturnsVisitor{};

template <class R, class Visitable, class... Others>
struct GenericFallbackReturnsVisitor<R, Visitable, Others...>: public GenericFallbackReturnsVisitor<R, Others...>
{
    explicit GenericFallbackReturnsVisitor(
        std::function<R(Visitable&)> _visitor,
        std::function<R(Others&)>... _otherVisitors
    ):
        GenericFallbackReturnsVisitor<R, Others...>(std::move(_otherVisitors)...),
        m_visitor(std::move(_visitor))
    {}

    using GenericFallbackReturnsVisitor<R, Others...>::operator ();
    R operator()(Visitable& _v) const { return m_visitor(_v); }

    std::function<R(Visitable&)> m_visitor;
};
template <class R>
struct GenericFallbackReturnsVisitor<R>: public boost::static_visitor<R> {
    template <class T>
    R operator()(T&) const { return {}; }
};

}