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