130 lines
2.6 KiB
C++
130 lines
2.6 KiB
C++
// -*- mode: c++; c-indent-level: 4; c++-member-init-indent: 8; comment-column: 35; -*-
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/*
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(c) Thales group, 2013
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation;
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version 2 of the License.
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This library 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 GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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Contact: http://eodev.sourceforge.net
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Authors:
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Lionel Parreaux <lionel.parreaux@gmail.com>
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*/
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/**
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A utility class for wrapping non-const references and use them as default arguments in functions.
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This especially is useful for avoiding constructor multiplication.
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For example, this is not valid C++98 code:
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\code
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struct MyClass {
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MyClass(T& my_T = default_T)
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: actual_T(my_T)
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{ }
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private:
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T default_T;
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T& actual_T;
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};
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\endcode
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This is the same code using eoOptional, which is valid:
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\code
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struct MyClass {
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MyClass(eoOptional<T> my_T = NULL)
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: actual_T(my_T.getOr(default_T))
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{ }
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private:
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T default_T;
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T& actual_T;
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};
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\endcode
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And from the point of view of the user, it is transparent:
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\code
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// Three ways of using MyClass:
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MyClass mc1;
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MyClass mc2(NULL);
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T t;
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MyClass mc3(t);
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\endcode
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@ingroup Utilities
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@{
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*/
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#ifndef _EOOPTIONAL_H
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#define _EOOPTIONAL_H
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#include <stdexcept>
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#include <eoObject.h>
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//#include <eoExceptions.h>
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template< class T >
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class eoOptional {
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public:
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static const eoOptional<T> null; // = eoOptional<T>();
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eoOptional (T& init)
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: _val(&init)
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{ }
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// used mainly for converting NULL to this class
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eoOptional (T* init)
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: _val(init)
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{ }
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bool hasValue() const
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{
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return _val != NULL;
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}
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T& get () const
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{
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if (!hasValue())
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throw std::runtime_error("Cannot get a reference from a eoOptional wrapper with no value");
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//throw eoEx;
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return *_val;
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}
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T& getOr (T& defaultValue) const
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{
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return hasValue()? *_val: defaultValue;
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}
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protected:
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eoOptional ()
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: _val(NULL)
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{ }
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private:
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T* _val;
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};
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template< class T >
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const eoOptional<T> eoOptional<T>::null = eoOptional<T>();
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#endif // _EOOPTIONAL_H
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/** @} */
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