65 lines
2.3 KiB
C++
65 lines
2.3 KiB
C++
/*
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NO-INSTANCE.hpp - marker for pure metaprogramming types
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Copyright (C) Lumiera.org
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2011, Hermann Vosseler <Ichthyostega@web.de>
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This program is free software; you can redistribute it and/or
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modify it under the terms of the GNU General Public License as
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published by the Free Software Foundation; either version 2 of
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the License, or (at your option) any later version.
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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 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., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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/** @file no-instance.hpp
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** Metaprogramming helper to prevent an entity to be ever instantiated at runtime.
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** For Template Metaprogramming, we often define classes for the sole purpose of
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** forming a distinct type. Such helper types are established during compilation
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** and typically trigger the instantiation of further types from templates, while
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** there is never the intention to emit any actual code from these entities.
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** As a safety measure, such _stricly metaprogramming related_ facilities may be
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** marked to provoke a compilation failure, when the compiler -- accidentally --
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** attempts to generate code to incorporate such an entity into the runtime world.
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**
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** \par example
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** The classical example is a marker type used to select one of various implementation
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** flavours of a given facility. In fact this helper was created to mark variations
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** based on the time code format in use.
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** @see timecode.hpp
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*/
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#ifndef LIB_META_NO_INSTANCE_H
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#define LIB_META_NO_INSTANCE_H
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#include <boost/static_assert.hpp>
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namespace lib {
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namespace meta{
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/**
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* An Entity never to be instantiated.
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* Marker baseclass for elements used in metaprogramming only.
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* Every attempt to instantiate such an element will cause an
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* compilation failure
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*/
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template<class X>
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struct NoInstance
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{
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NoInstance() { BOOST_STATIC_ASSERT(!sizeof(X)); }
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NoInstance (NoInstance const&) { BOOST_STATIC_ASSERT(!sizeof(X)); }
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};
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}} // namespace lib::meta
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#endif
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