expressionTraits.hpp

/*
 * CoDiPack, a Code Differentiation Package
 *
 * Copyright (C) 2015-2026 Chair for Scientific Computing (SciComp), University of Kaiserslautern-Landau
 * Homepage: http://scicomp.rptu.de
 * Contact:  Prof. Nicolas R. Gauger (codi@scicomp.uni-kl.de)
 *
 * Lead developers: Max Sagebaum, Johannes Blühdorn (SciComp, University of Kaiserslautern-Landau)
 *
 * This file is part of CoDiPack (http://scicomp.rptu.de/software/codi).
 *
 * CoDiPack 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.
 *
 * CoDiPack 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 CoDiPack.
 * If not, see <http://www.gnu.org/licenses/>.
 *
 * For other licensing options please contact us.
 *
 * Authors:
 *  - SciComp, University of Kaiserslautern-Landau:
 *    - Max Sagebaum
 *    - Johannes Blühdorn
 *    - Former members:
 *      - Tim Albring
 */
#pragma once
 
#include <type_traits>
 
#include "../config.h"
#include "../expressions/logic/compileTimeTraversalLogic.hpp"
#include "../misc/macros.hpp"
#include "misc/enableIfHelpers.hpp"

namespace codi {
 
  template<typename T_Real, typename T_Impl>
  struct ExpressionInterface;
 
  template<typename T_Real, typename T_Gradient, typename T_Tape, typename T_Impl>
  struct LhsExpressionInterface;
 
  template<typename T_Real, template<typename> class T_ConversionOperator>
  struct ConstantExpression;
 
  template<typename T_Tape>
  struct StaticContextActiveType;
 
  namespace RealTraits {
    template<typename T_Real, typename>
    struct AggregatedTypeTraits;
  }
 
  template<typename T_Real>
  struct EmptyOperation;
 
  template<typename T_Real, template<typename> class T_Operation, typename... T_ArgExprs>
  struct ComputeExpression;

  namespace ExpressionTraits {
 
    /*******************************************************************************/

    template<typename... Logic>
    struct ValidateADLogicImpl;

    template<>
    struct ValidateADLogicImpl<> {
      public:

        using ADLogic = void;
    };

    template<typename Logic>
    struct ValidateADLogicImpl<Logic> {
      public:

        using ADLogic = Logic;
    };

    template<typename LogicA, typename LogicB>
    struct ValidateADLogicImpl<LogicA, LogicB> {
      private:
        static bool constexpr isAVoid = std::is_same<void, LogicA>::value;
        static bool constexpr isBVoid = std::is_same<void, LogicB>::value;
        static bool constexpr isBothVoid = isAVoid & isBVoid;
        static bool constexpr isBothSame = std::is_same<LogicA, LogicB>::value;
 
        // Either one can be void (aka. constant value) but not both otherwise both need to be the same.
        CODI_STATIC_ASSERT((!isBothVoid) & (!isAVoid | !isBVoid | isBothSame), "AD logic types need to be the same.");
 
      public:

        using ADLogic = typename std::conditional<isBVoid, LogicA, LogicB>::type;
    };

    template<typename LogicA, typename... LogicOther>
    struct ValidateADLogicImpl<LogicA, LogicOther...> {
      public:

        using ADLogic =
            typename ValidateADLogicImpl<LogicA, typename ValidateADLogicImpl<LogicOther...>::ADLogic>::ADLogic;
    };

    template<typename... Results>
    using ValidateADLogic = ValidateADLogicImpl<Results...>;

    template<typename T_Real, typename T_Tape, bool T_isStatic = false, typename = void>
    struct ActiveResultImpl {
        using Real = CODI_DD(T_Real, CODI_ANY);  
        using Tape = CODI_DD(T_Tape, CODI_ANY);  

        using ActiveResult = CODI_ANY;
    };

    template<typename Real, typename Tape, bool isStatic = false>
    using ActiveResult = typename ActiveResultImpl<Real, Tape, isStatic>::ActiveResult;

    /*******************************************************************************/

    template<typename Expr, typename = void>
    struct IsExpression : std::false_type {};
 
#ifndef DOXYGEN_DISABLE
    template<typename Expr>
    struct IsExpression<Expr, typename enable_if_base_of<ExpressionInterface<typename Expr::Real, Expr>, Expr>::type>
        : std::true_type {};
#endif

    template<typename Expr>
    bool constexpr isExpression = IsExpression<Expr>::value;

    template<typename Expr, typename T = void>
    using EnableIfExpression = typename std::enable_if<IsExpression<Expr>::value, T>::type;

    template<typename Expr, typename = void>
    struct IsLhsExpression : std::false_type {};
 
#ifndef DOXYGEN_DISABLE
    template<typename Expr>
    struct IsLhsExpression<
        Expr, typename enable_if_base_of<
                  LhsExpressionInterface<typename Expr::Real, typename Expr::Gradient, typename Expr::Tape, Expr>,
                  Expr>::type> : std::true_type {};
 
    template<typename Tape>
    struct IsLhsExpression<StaticContextActiveType<Tape>> : std::true_type {};
#endif

    template<typename Expr>
    bool constexpr isLhsExpression = IsLhsExpression<Expr>::value;

    template<typename Expr, typename T = void>
    using EnableIfLhsExpression = typename std::enable_if<IsLhsExpression<Expr>::value, T>::type;

    template<typename Expr>
    struct IsConstantExpression : std::false_type {};
 
#ifndef DOXYGEN_DISABLE
    template<typename Real, template<typename> class ConversionOperator>
    struct IsConstantExpression<ConstantExpression<Real, ConversionOperator>> : std::true_type {};
#endif
 
    template<typename Expr>
    bool constexpr isConstantExpression = IsConstantExpression<Expr>::value;

    template<typename Expr, typename T = void>
    using EnableIfConstantExpression = typename std::enable_if<IsConstantExpression<Expr>::value, T>::type;

    template<typename Expr>
    struct IsEmptyExpression : std::false_type {};
 
#ifndef DOXYGEN_DISABLE
    template<typename Real>
    struct IsEmptyExpression<ComputeExpression<Real, EmptyOperation>> : std::true_type {};
#endif
 
    template<typename Expr>
    bool constexpr isEmptyExpression = IsEmptyExpression<Expr>::value;

    template<typename Expr, typename T = void>
    using EnableIfEmptyExpression = typename std::enable_if<IsEmptyExpression<Expr>::value, T>::type;

    template<typename Expr>
    struct IsStaticContextActiveType : std::false_type {};
 
#ifndef DOXYGEN_DISABLE
    template<typename Tape>
    struct IsStaticContextActiveType<StaticContextActiveType<Tape>> : std::true_type {};
#endif

    template<typename Expr>
    bool constexpr isStaticContextActiveType = IsStaticContextActiveType<Expr>::value;

    template<typename Expr, typename T = void>
    using EnableIfStaticContextActiveType = typename std::enable_if<IsStaticContextActiveType<Expr>::value, T>::type;

    /*******************************************************************************/

    template<typename Expr>
    struct NumberOfActiveTypeArguments : public CompileTimeTraversalLogic<size_t, NumberOfActiveTypeArguments<Expr>> {
      public:

        using Base = CompileTimeTraversalLogic<size_t, NumberOfActiveTypeArguments<Expr>>;

        template<typename Node, typename = ExpressionTraits::EnableIfLhsExpression<Node>>
        CODI_INLINE static size_t constexpr leaf() {
          return 1;
        }
        using CompileTimeTraversalLogic<size_t, NumberOfActiveTypeArguments>::leaf;

        static size_t constexpr value = Base::template eval<Expr>();
    };

    template<typename Expr>
    bool constexpr numberOfActiveTypeArguments = NumberOfActiveTypeArguments<Expr>::value;

    template<typename Expr>
    struct NumberOfConstantTypeArguments
        : public CompileTimeTraversalLogic<size_t, NumberOfConstantTypeArguments<Expr>> {
      public:

        using Base = CompileTimeTraversalLogic<size_t, NumberOfConstantTypeArguments<Expr>>;

        template<typename Node, typename = EnableIfConstantExpression<Node>>
        CODI_INLINE static size_t constexpr leaf() {
          return ::codi::RealTraits::AggregatedTypeTraits<typename Node::Real, void>::Elements;
        }
        using CompileTimeTraversalLogic<size_t, NumberOfConstantTypeArguments>::leaf;

        static size_t constexpr value = Base::template eval<Expr>();
    };

    template<typename Expr>
    bool constexpr numberOfConstantTypeArguments = NumberOfConstantTypeArguments<Expr>::value;

    template<typename Expr>
    struct NumberOfOperations : public CompileTimeTraversalLogic<size_t, NumberOfOperations<Expr>> {
      public:

        template<typename Node>
        CODI_INLINE static size_t constexpr node() {
          return 1 + NumberOfOperations::template toLinks<Node>();
        }

        static size_t constexpr value = NumberOfOperations::template eval<Expr>();
    };

    template<typename Expr>
    bool constexpr numberOfOperations = NumberOfOperations<Expr>::value;

  }
}