1 2 /** 3 * Copyright (C) 2018-present MongoDB, Inc. 4 * 5 * This program is free software: you can redistribute it and/or modify 6 * it under the terms of the Server Side Public License, version 1, 7 * as published by MongoDB, Inc. 8 * 9 * This program is distributed in the hope that it will be useful, 10 * but WITHOUT ANY WARRANTY; without even the implied warranty of 11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 * Server Side Public License for more details. 13 * 14 * You should have received a copy of the Server Side Public License 15 * along with this program. If not, see 16 * <http://www.mongodb.com/licensing/server-side-public-license>. 17 * 18 * As a special exception, the copyright holders give permission to link the 19 * code of portions of this program with the OpenSSL library under certain 20 * conditions as described in each individual source file and distribute 21 * linked combinations including the program with the OpenSSL library. You 22 * must comply with the Server Side Public License in all respects for 23 * all of the code used other than as permitted herein. If you modify file(s) 24 * with this exception, you may extend this exception to your version of the 25 * file(s), but you are not obligated to do so. If you do not wish to do so, 26 * delete this exception statement from your version. If you delete this 27 * exception statement from all source files in the program, then also delete 28 * it in the license file. 29 */ 30 31 #pragma once 32 33 #include <cstring> 34 35 #include "mongo/base/data_view.h" 36 37 namespace mongo { 38 39 struct ZeroInitTag_t { ZeroInitTag_tZeroInitTag_t40 ZeroInitTag_t(){}; 41 }; 42 43 const ZeroInitTag_t kZeroInitTag; 44 45 template <typename Layout, typename ConstView, typename View> 46 class EncodedValueStorage { 47 protected: EncodedValueStorage()48 EncodedValueStorage() {} 49 50 // This explicit constructor is provided to allow for easy zeroing 51 // during creation of a value. You might prefer this over an 52 // uninitialised value if the zeroed version provides a useful base 53 // state. Such cases might include a set of counters that begin at 54 // zero, flags that start off false or a larger structure where some 55 // significant portion of storage falls into those kind of use cases. 56 // Use this where you might have used calloc(1, sizeof(type)) in C. 57 // 58 // The added value of providing it as a constructor lies in the ability 59 // of subclasses to easily inherit a zeroed base state during 60 // initialization. EncodedValueStorage(ZeroInitTag_t)61 explicit EncodedValueStorage(ZeroInitTag_t) { 62 std::memset(_data, 0, sizeof(_data)); 63 } 64 65 public: view()66 View view() { 67 return _data; 68 } 69 constView()70 ConstView constView() const { 71 return _data; 72 } 73 View()74 operator View() { 75 return view(); 76 } 77 ConstView()78 operator ConstView() const { 79 return constView(); 80 } 81 82 private: 83 char _data[sizeof(Layout)]; 84 }; 85 86 } // namespace mongo 87