visitor.h

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/* 
* Copyright (C) 2020-2026 MEmilio
*
* Authors: Daniel Abele
*
* Contact: Martin J. Kuehn <Martin.Kuehn@DLR.de>
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*     http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef VISITOR_H
#define VISITOR_H
 
namespace mio
{
 
template <typename... Types>
struct Visitor;
 
template <typename T>
struct Visitor<T> {
    virtual void visit(T& t) = 0;
 
    virtual ~Visitor() = default;
};
 
template <typename T, typename... Types>
struct Visitor<T, Types...> : public Visitor<Types...> // Recursive
{
    using Visitor<Types...>::visit;
    virtual void visit(T& t) = 0;
 
    virtual ~Visitor() = default;
};
 
template <typename... Types>
struct ConstVisitor;
 
template <typename T>
struct ConstVisitor<T> {
    virtual void visit(const T& t) = 0;
 
    virtual ~ConstVisitor() = default;
};
 
template <typename T, typename... Types>
struct ConstVisitor<T, Types...> : public ConstVisitor<Types...> // Recursive
{
    using ConstVisitor<Types...>::visit;
    virtual void visit(const T& t) = 0;
 
    virtual ~ConstVisitor() = default;
};
 
template <class Derived, class Base, class Visitor, class ConstVisitor>
struct Visitable : public Base {
    using Base::Base;
 
    void accept(Visitor& visitor)
    {
        visitor.visit(*static_cast<Derived*>(this));
    }
    void accept(ConstVisitor& visitor) const
    {
        visitor.visit(*static_cast<Derived const*>(this));
    }
};
 
} // namespace mio
 
#endif // VISITOR_H