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86 lines
2.0 KiB
86 lines
2.0 KiB
// (C) Copyright David Abrahams 2002. |
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// (C) Copyright Jeremy Siek 2002. |
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// (C) Copyright Thomas Witt 2002. |
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// Distributed under the Boost Software License, Version 1.0. (See |
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// accompanying file LICENSE_1_0.txt or copy at |
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// http://www.boost.org/LICENSE_1_0.txt) |
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#ifndef BOOST_ENABLE_IF_23022003THW_HPP |
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#define BOOST_ENABLE_IF_23022003THW_HPP |
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#include <boost/detail/workaround.hpp> |
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#include <boost/mpl/identity.hpp> |
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#include <boost/iterator/detail/config_def.hpp> |
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// |
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// Boost iterators uses its own enable_if cause we need |
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// special semantics for deficient compilers. |
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// 23/02/03 thw |
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// |
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namespace boost |
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{ |
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namespace iterators |
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{ |
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// |
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// Base machinery for all kinds of enable if |
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// |
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template<bool> |
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struct enabled |
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{ |
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template<typename T> |
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struct base |
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{ |
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typedef T type; |
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}; |
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}; |
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// |
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// For compilers that don't support "Substitution Failure Is Not An Error" |
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// enable_if falls back to always enabled. See comments |
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// on operator implementation for consequences. |
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// |
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template<> |
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struct enabled<false> |
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{ |
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template<typename T> |
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struct base |
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{ |
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#ifdef BOOST_NO_SFINAE |
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typedef T type; |
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// This way to do it would give a nice error message containing |
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// invalid overload, but has the big disadvantage that |
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// there is no reference to user code in the error message. |
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// |
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// struct invalid_overload; |
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// typedef invalid_overload type; |
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// |
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#endif |
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}; |
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}; |
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template <class Cond, |
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class Return> |
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struct enable_if |
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# if !defined(BOOST_NO_SFINAE) && !defined(BOOST_NO_IS_CONVERTIBLE) |
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: enabled<(Cond::value)>::template base<Return> |
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# else |
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: mpl::identity<Return> |
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# endif |
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{ |
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# if BOOST_WORKAROUND(BOOST_MSVC, < 1300) |
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typedef Return type; |
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# endif |
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}; |
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} // namespace iterators |
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} // namespace boost |
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#include <boost/iterator/detail/config_undef.hpp> |
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#endif // BOOST_ENABLE_IF_23022003THW_HPP
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