| /** |
| * Copyright 2015 Pivotal Software, Inc. |
| * Copyright 2015 Pivotal Software, Inc. |
| * |
| * 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 QUICKSTEP_TYPES_NULLTYPE_HPP_ |
| #define QUICKSTEP_TYPES_NULLTYPE_HPP_ |
| |
| #include <cstddef> |
| #include <cstdio> |
| #include <string> |
| |
| #include "types/Type.hpp" |
| #include "types/TypeID.hpp" |
| #include "utility/Macros.hpp" |
| |
| #include "glog/logging.h" |
| |
| namespace quickstep { |
| |
| class TypedValue; |
| |
| /** \addtogroup Types |
| * @{ |
| */ |
| |
| /** |
| * @brief A special type that can ONLY represent NULL values and can be coerced |
| * to any other nullable Type. It is used in the expression system and |
| * optimizer to represent NULL literals that appear in queries where |
| * a Type hint can not be immediately deduced from context and schema. |
| * @note NullType can not be used as an argument type for any operations or |
| * comparisons, however it can be implicitly cast to whatever input type |
| * a particular operation may accept. It is also assumed that applying |
| * any operation to an argument of NullType always yields NULL values. |
| **/ |
| class NullType : public Type { |
| public: |
| static const TypeID kStaticTypeID = kNullType; |
| |
| /** |
| * @brief Get a reference to the nullable singleton instance of this Type. |
| * @note Unlike other Types, there is no corresponding method to get a |
| * non-nullable version of NullType. NullType is ALWAYS nullable. |
| * |
| * @return A reference to the nullable singleton instance of this Type. |
| **/ |
| static const NullType& InstanceNullable() { |
| static NullType instance; |
| return instance; |
| } |
| |
| const Type& getNullableVersion() const override { |
| return InstanceNullable(); |
| } |
| |
| const Type& getNonNullableVersion() const override { |
| LOG(FATAL) << "Called NullType::getNonNullableVersion(), which is not allowed."; |
| } |
| |
| std::size_t estimateAverageByteLength() const override { |
| return 0; |
| } |
| |
| bool isCoercibleFrom(const Type &original_type) const override { |
| return original_type.getTypeID() == kNullType; |
| } |
| |
| bool isSafelyCoercibleFrom(const Type &original_type) const override { |
| return original_type.getTypeID() == kNullType; |
| } |
| |
| int getPrintWidth() const override { |
| return 0; |
| } |
| |
| std::string printValueToString(const TypedValue &value) const override { |
| LOG(FATAL) << "NullType is not printable"; |
| } |
| |
| void printValueToFile(const TypedValue &value, |
| FILE *file, |
| const int padding = 0) const override { |
| LOG(FATAL) << "NullType is not printable"; |
| } |
| |
| bool parseValueFromString(const std::string &value_string, |
| TypedValue *value) const override { |
| return false; |
| } |
| |
| private: |
| // NOTE(chasseur): NullType requires 0 bytes of inherent storage. It does, |
| // however, require a bit in NULL bitmaps. |
| NullType() : Type(Type::kOther, kNullType, true, 0, 0) { |
| } |
| |
| DISALLOW_COPY_AND_ASSIGN(NullType); |
| }; |
| |
| /** @} */ |
| |
| } // namespace quickstep |
| |
| #endif // QUICKSTEP_TYPES_NULLTYPE_HPP_ |