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108 lines
3.0 KiB
108 lines
3.0 KiB
5 months ago
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#ifndef NULLABLE_INCLUDED
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#define NULLABLE_INCLUDED
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/*
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Copyright (c) 2014, 2017, Oracle and/or its affiliates. All rights reserved.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License, version 2.0,
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as published by the Free Software Foundation.
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This program is also distributed with certain software (including
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but not limited to OpenSSL) that is licensed under separate terms,
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as designated in a particular file or component or in included license
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documentation. The authors of MySQL hereby grant you an additional
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permission to link the program and your derivative works with the
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separately licensed software that they have included with MySQL.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License, version 2.0, for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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/**
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@file include/nullable.h
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*/
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#include "my_dbug.h"
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namespace Mysql {
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/**
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Class for storing value or NULL value.
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*/
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template <typename T_value>
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class Nullable {
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public:
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Nullable() : m_has_value(false) {}
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Nullable(T_value value) : m_has_value(true), m_value(value) {}
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Nullable(const Nullable<T_value> &other)
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: m_has_value(other.m_has_value), m_value(other.m_value) {}
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/**
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Assigns value from another Nullable<> object.
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*/
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Nullable<T_value> &operator=(const Nullable<T_value> &other) {
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this->m_has_value = other.m_has_value;
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if (this->m_has_value) {
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this->m_value = other.m_value;
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}
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return *this;
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}
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/**
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Compares two Nullable<> objects for equality.
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*/
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bool operator==(const Nullable<T_value> &other) const {
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if (this->has_value() != other.has_value())
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return false;
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else if (this->has_value() && this->value() != other.value())
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return false;
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return true;
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}
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/**
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Compares two Nullable<> objects for in-equality.
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*/
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bool operator!=(const Nullable<T_value> &other) const {
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return !(*this == other);
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}
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/**
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Returns true if object has not-NULL value assigned. If this is false, one
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should not try to get value by value().
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*/
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bool has_value() const { return this->m_has_value; }
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/**
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Returns actual value of object. Do not call this method if has_value()
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returns false.
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*/
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const T_value &value() const {
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DBUG_ASSERT(this->m_has_value);
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return this->m_value;
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}
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private:
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/**
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Specifies if this object represents NULL value. If this is false, one
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should not try to get value by value().
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*/
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bool m_has_value;
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/**
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Actual value, if m_has_value is true. Undefined if m_has_value is false.
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*/
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T_value m_value{};
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};
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} // namespace Mysql
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#endif // NULLABLE_INCLUDED
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