type_traits.hpp

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/*
 *   Copyright 2021 Huawei Technologies Co., Ltd.
 *
 * 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 _H_GRB_TYPE_TRAITS
#define _H_GRB_TYPE_TRAITS

#include <type_traits>


namespace grb {

    template< typename T >
    struct is_container {

        static const constexpr bool value = false;

    };

    template< typename T >
    struct is_semiring {

        static const constexpr bool value = false;

    };

    template< typename T >
    struct is_monoid {

        static const constexpr bool value = false;

    };

    template< typename T >
    struct is_operator {

        static const constexpr bool value = false;
    };

    template< typename T >
    struct is_object {

        static const constexpr bool value = is_container< T >::value ||
            is_semiring< T >::value ||
            is_monoid< T >::value ||
            is_operator< T >::value;
    };

    template< typename T, typename = void >
    struct is_idempotent {

        static_assert( is_operator< T >::value || is_monoid< T >::value,
            "Template argument to grb::is_idempotent must be an operator or a monoid!" );

        static const constexpr bool value = false;

    };

    template< typename Monoid >
    struct is_idempotent<
        Monoid,
        typename std::enable_if< is_monoid< Monoid >::value, void >::type
    > {
        static const constexpr bool value =
            is_idempotent< typename Monoid::Operator >::value;
    };

    template< typename T, typename = void >
    struct is_associative {

        static_assert( is_operator< T >::value || is_monoid< T >::value,
            "Template argument should be an ALP binary operator or monoid." );

        static const constexpr bool value = false;

    };

    template< typename Monoid >
    struct is_associative<
        Monoid,
        typename std::enable_if< is_monoid< Monoid >::value, void >::type
    > {
        static_assert( is_associative< typename Monoid::Operator >::value,
            "Malformed ALP monoid encountered" );
        static const constexpr bool value = true;
    };

    template< typename T, typename = void >
    struct is_commutative {

        static_assert( is_operator< T >::value || is_monoid< T >::value,
            "Template argument should be an ALP binary operator or monoid." );

        static const constexpr bool value = false;

    };

    template< typename Monoid >
    struct is_commutative<
        Monoid,
        typename std::enable_if< is_monoid< Monoid >::value, void >::type
    > {
        static const constexpr bool value =
            is_commutative< typename Monoid::Operator >::value;
    };

    template< typename T >
    struct has_immutable_nonzeroes {

        static_assert( is_semiring< T >::value,
            "Template argument to grb::has_immutable_nonzeroes must be a "
            "semiring!" );

        static const constexpr bool value = false;

    };

    namespace internal {

        template< typename OP >
        struct maybe_noop {
            static_assert( is_operator< OP >::value,
                "Argument to internal::maybe_noop must be an operator."
            );
            static const constexpr bool value = false;
        };

    } // end namespace grb::internal

} // namespace grb

#endif // end _H_GRB_TYPE_TRAITS