77 lines
2.4 KiB
C
77 lines
2.4 KiB
C
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// Copyright (c) 2012 GeometryFactory Sarl (France)
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// All rights reserved.
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//
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// $URL: https://github.com/CGAL/cgal/blob/v5.1/STL_Extension/include/CGAL/is_streamable.h $
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// $Id: is_streamable.h 0779373 2020-03-26T13:31:46+01:00 Sébastien Loriot
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// SPDX-License-Identifier: BSL-1.0
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//
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// Author(s) : Laurent Rineau, Philipp Moeller
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#ifndef CGAL_IS_STREAMABLE_H
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#define CGAL_IS_STREAMABLE_H
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#include <boost/type_traits/remove_reference.hpp>
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#include <boost/type_traits/remove_cv.hpp>
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#include <boost/static_assert.hpp>
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#include <iostream>
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namespace CGAL {
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namespace internal {
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namespace is_streamable
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{
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// A tag type returned by operator == for the any struct in this namespace
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// when T does not support ==.
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struct tag {};
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// This type soaks up any implicit conversions and makes the following operator ==
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// less preferred than any other such operator found via ADL.
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struct any
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{
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// Conversion constructor for any type.
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template <class T>
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any(T const&);
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};
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tag operator<<(any const&, any const&);
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tag operator>>(any const&, any const&);
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// Two overloads to distinguish whether T supports a certain operator expression.
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// The first overload returns a reference to a two-element character array and is chosen if
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// T does not support the expression, such as ==, whereas the second overload returns a char
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// directly and is chosen if T supports the expression. So using sizeof(check(<expression>))
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// returns 2 for the first overload and 1 for the second overload.
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typedef char yes;
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typedef char (&no)[2];
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no check(tag);
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template <class T>
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yes check(T const&);
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template <class T>
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struct is_streamable_impl
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{
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static typename boost::remove_cv<typename boost::remove_reference<T>::type>::type const & x;
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static typename boost::remove_cv<typename boost::remove_reference<T>::type>::type & y;
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static const bool value =
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sizeof(is_streamable::check(std::cout << x)) == sizeof(is_streamable::yes) &&
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sizeof(is_streamable::check(std::cin >> y)) == sizeof(is_streamable::yes);
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};
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} // end namespace internal::is_streamable
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} // end namespace internal
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/// is_streamable is a meta-function that checks if a type is streamable
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///
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/// is_streamable<T>::value is true iff the type T has stream operators <<
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/// and >>. Otherwise it is false.
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template <class T>
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struct is_streamable
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: internal::is_streamable::is_streamable_impl<T> {};
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} // end namespace CGAL
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#endif // CGAL_IS_STREAMABLE_H
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