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Add singleton_base with test (#1002)
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‎include/etl/file_error_numbers.h‎

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#define ETL_EXPECTED_FILE_ID "70"
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#define ETL_ALIGNMENT_FILE_ID "71"
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#define ETL_BASE64_FILE_ID "72"
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#define ETL_SINGLETON_BASE_FILE_ID "73"
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#endif

‎include/etl/singleton_base.h‎

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///\file
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/******************************************************************************
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The MIT License(MIT)
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Embedded Template Library.
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https://github.com/ETLCPP/etl
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https://www.etlcpp.com
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Copyright(c) 2019 John Wellbelove
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Copyright(c) 2024 BMW AG
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Permission is hereby granted, free of charge, to any person obtaining a copy
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of this software and associated documentation files(the "Software"), to deal
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in the Software without restriction, including without limitation the rights
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to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
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copies of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions :
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The above copyright notice and this permission notice shall be included in all
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copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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SOFTWARE.
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******************************************************************************/
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#ifndef ETL_SINGLETON_BASE_INCLUDED
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#define ETL_SINGLETON_BASE_INCLUDED
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///\defgroup singleton_base singleton_base
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/// Templated version of the singleton pattern, implemented as base class
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/// for singletons.
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///\ingroup etl
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#include "platform.h"
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#include "error_handler.h"
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#include "file_error_numbers.h"
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namespace etl
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{
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//*************************************************************************
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/// Base singleton error exception.
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//*************************************************************************
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class singleton_base_exception : public etl::exception
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{
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public:
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singleton_base_exception(string_type reason_, string_type file_name_, numeric_type line_number_)
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: exception(reason_, file_name_, line_number_)
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{
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}
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};
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//*************************************************************************
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/// Singleton not created error exception.
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//*************************************************************************
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class singleton_base_not_created : public etl::singleton_base_exception
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{
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public:
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singleton_base_not_created(string_type file_name_, numeric_type line_number_)
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: singleton_base_exception(ETL_ERROR_TEXT("singleton_base:not created", ETL_SINGLETON_BASE_FILE_ID"A"), file_name_, line_number_)
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{
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}
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};
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//*************************************************************************
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/// Singleton instance already exists.
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//*************************************************************************
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class singleton_base_already_created : public etl::singleton_base_exception
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{
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public:
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singleton_base_already_created(string_type file_name_, numeric_type line_number_)
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: singleton_base_exception(ETL_ERROR_TEXT("singleton_base:already created", ETL_SINGLETON_BASE_FILE_ID"A"), file_name_, line_number_)
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{
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}
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};
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//***********************************************************************
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/// Base class for singletons.
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/// \tparam T Any type that wants to expose the instance() interface.
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///
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/// This class is designed to work as a generic base class for any class that wants to
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/// provide a singleton interface. It'll also work for classes that do not have a
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/// default constructor.
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///
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/// Usage example:
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///
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/// class Origin
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/// : singleton<Origin>
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/// {
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/// public:
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/// Origin(int x, int y)
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/// : singleton<Origin>(*this)
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/// {}
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///
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/// int getX() const;
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/// } theOrigin(0, 0);
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///
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/// int x = Origin::instance().getX();
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///
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///
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/// Note:
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///
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/// It is important that a call to instance() will not create the instance of the class. It needs
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/// to be created by the user before calling instance(). This way, the user has better control
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/// over the instance lifetime instead of e.g. lazy initialization.
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//***********************************************************************
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template<class T>
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class singleton_base
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{
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protected:
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//***********************************************************************
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/// Constructs the instance of singleton.
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/// theInstance Reference to T, which will be returned when instance() is called.
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//***********************************************************************
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explicit singleton_base(T& theInstance)
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{
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ETL_ASSERT(m_self == nullptr, ETL_ERROR(etl::singleton_base_already_created));
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m_self = &theInstance;
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}
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//***********************************************************************
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/// Removes the internal reference to the instance passed in the constructor.
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//***********************************************************************
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~singleton_base() { m_self = nullptr; }
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public:
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//***********************************************************************
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// Returns a reference to the instance.
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//***********************************************************************
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static T& instance()
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{
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ETL_ASSERT(m_self != nullptr, ETL_ERROR(etl::singleton_base_not_created));
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return *m_self;
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}
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//***********************************************************************
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/// Returns whether an instance has been attached to singleton<T> or not.
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//***********************************************************************
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static bool is_valid() { return (m_self != nullptr); }
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private:
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static T* m_self;
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};
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//***********************************************************************
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/// No violation of one definition rule as this is a class template
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//***********************************************************************
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template<class T>
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T* singleton_base<T>::m_self = nullptr;
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}
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#endif

‎test/test_singleton_base.cpp‎

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/******************************************************************************
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The MIT License(MIT)
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Embedded Template Library.
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https://github.com/ETLCPP/etl
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https://www.etlcpp.com
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Copyright(c) 2022 John Wellbelove
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Copyright(c) 2024 BMW AG
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Permission is hereby granted, free of charge, to any person obtaining a copy
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of this software and associated documentation files(the "Software"), to deal
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in the Software without restriction, including without limitation the rights
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to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
15+
copies of the Software, and to permit persons to whom the Software is
16+
furnished to do so, subject to the following conditions :
17+
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The above copyright notice and this permission notice shall be included in all
19+
copies or substantial portions of the Software.
20+
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
22+
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
23+
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
24+
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
25+
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
26+
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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SOFTWARE.
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******************************************************************************/
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#include "unit_test_framework.h"
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#include "etl/singleton_base.h"
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#include <string>
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#include <type_traits>
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class Test_Singleton: public ::etl::singleton_base<Test_Singleton>
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{
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public:
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Test_Singleton(int i_, std::string text_)
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: ::etl::singleton_base<Test_Singleton>(*this)
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, i(i_)
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, text(text_)
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{
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}
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void Increment()
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{
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++i;
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text += "*";
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}
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int i;
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std::string text;
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};
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namespace
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{
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SUITE(test_singleton)
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{
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//*************************************************************************
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TEST(test1)
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{
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CHECK(!Test_Singleton::is_valid());
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CHECK_THROW(Test_Singleton::instance(), etl::singleton_base_not_created);
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{
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Test_Singleton singleton(1, "Start:");
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CHECK(Test_Singleton::is_valid());
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Test_Singleton& ts = Test_Singleton::instance();
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CHECK_EQUAL(1, ts.i);
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CHECK_EQUAL("Start:", ts.text);
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ts.Increment();
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CHECK_EQUAL(2, ts.i);
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CHECK_EQUAL("Start:*", ts.text);
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Test_Singleton* pts = &Test_Singleton::instance();
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CHECK_EQUAL(2, ts.i);
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CHECK_EQUAL(2, pts->i);
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CHECK_EQUAL("Start:*", ts.text);
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CHECK_EQUAL("Start:*", pts->text);
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pts->Increment();
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CHECK_EQUAL(3, ts.i);
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CHECK_EQUAL(3, pts->i);
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CHECK_EQUAL("Start:**", ts.text);
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CHECK_EQUAL("Start:**", pts->text);
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CHECK_THROW(Test_Singleton(2, "XYZ"), etl::singleton_base_already_created);
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}
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CHECK(!Test_Singleton::is_valid());
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CHECK_THROW(Test_Singleton::instance(), etl::singleton_base_not_created);
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}
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}
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}
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