112 lines
3.3 KiB
C++
112 lines
3.3 KiB
C++
/*
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UTIL.hpp - metaprogramming helpers and utilities
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Copyright (C) Lumiera.org
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2008, 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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#ifndef LUMIERA_META_UTIL_H
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#define LUMIERA_META_UTIL_H
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namespace lumiera {
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/* types for figuring out the overload resolution chosen by the compiler */
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typedef char Yes_t;
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struct No_t { char padding[8]; };
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namespace typelist {
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/** Compile-time Type equality:
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* Simple Trait template to pick up types considered
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* \em identical by the compiler.
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* @warning identical, not sub-type!
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*/
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template<typename T1, typename T2>
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class is_sameType
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{
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static const bool value = false;
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};
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template<typename T>
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class is_sameType<T,T>
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{
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static const bool value = true;
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};
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/** semi-automatic detection if an instantiation is possible.
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* Requires help by the template to be tested, which needs to define
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* a typedef member \c is_defined. The embedded metafunction Test can be used
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* as a predicate for filtering types which may yield a valid instantiation
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* of the candidate template in question.
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* \par
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* A fully automated solution for this problem is impossible by theoretic reasons.
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* Any non trivial use of such a \c is_defined trait would break the "One Definition Rule",
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* as the state of any type can change from "partially defined" to "fully defined" over
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* the course of any translation unit. Thus, even if there may be a \em solution out there,
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* we can expect it to break at some point by improvements/fixes to the C++ Language.
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*/
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template<template<class> class _CandidateTemplate_>
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struct Instantiation
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{
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template<class X>
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class Test
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{
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typedef _CandidateTemplate_<X> Instance;
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template<class U>
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static Yes_t check(typename U::is_defined *);
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template<class U>
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static No_t check(...);
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public:
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static const bool value = (sizeof(Yes_t)==sizeof(check<Instance>(0)));
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};
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};
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/** Trait template for detecting a typelist type.
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* For example, this allows to write specialisations with the help of
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* boost::enable_if
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*/
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template<typename TY>
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class is_Typelist
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{
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template<class X>
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static Yes_t check(typename X::List *);
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template<class>
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static No_t check(...);
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public:
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static const bool value = (sizeof(Yes_t)==sizeof(check<TY>(0)));
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};
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} // namespace typelist
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} // namespace lumiera
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#endif
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