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Extracted is_iterator trait to a separate header.

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Also, reworked is_iterator to be more robust against various corner cases
and added dedicated tests for the type trait.
This commit is contained in:
Andrey Semashev
2023-05-21 00:18:27 +03:00
parent e8fbd92a61
commit 85b542e1b6
4 changed files with 317 additions and 44 deletions
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47
include/boost/next_prior.hpp
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@@ -15,13 +15,12 @@
#ifndef BOOST_NEXT_PRIOR_HPP_INCLUDED
#define BOOST_NEXT_PRIOR_HPP_INCLUDED
#include <iterator>
#include <boost/config.hpp>
#include <boost/core/enable_if.hpp>
#include <boost/type_traits/has_plus.hpp>
#include <boost/type_traits/has_plus_assign.hpp>
#include <boost/type_traits/has_minus.hpp>
#include <boost/type_traits/has_minus_assign.hpp>
#include <boost/iterator/is_iterator.hpp>
#include <boost/iterator/advance.hpp>
#include <boost/iterator/reverse_iterator.hpp>
@@ -39,46 +38,6 @@ namespace boost {
namespace next_prior_detail {
// The trait attempts to detect if the T type is an iterator. Class-type iterators are assumed
// to have the nested type iterator_category. Strictly speaking, this is not required to be the
// case (e.g. a user can specialize iterator_traits for T without defining T::iterator_category).
// Still, this is a good heuristic in practice, and we can't do anything better anyway.
// Since C++17 we can test for iterator_traits<T>::iterator_category presence instead as it is
// required to be only present for iterators.
template< typename T, typename Void = void >
struct is_iterator_class
{
static BOOST_CONSTEXPR_OR_CONST bool value = false;
};
template< typename T >
struct is_iterator_class<
T,
typename enable_if_has_type<
#if !defined(BOOST_NO_CXX17_ITERATOR_TRAITS)
typename std::iterator_traits< T >::iterator_category
#else
typename T::iterator_category
#endif
>::type
>
{
static BOOST_CONSTEXPR_OR_CONST bool value = true;
};
template< typename T >
struct is_iterator :
public is_iterator_class< T >
{
};
template< typename T >
struct is_iterator< T* >
{
static BOOST_CONSTEXPR_OR_CONST bool value = true;
};
template< typename T, typename Distance, bool HasPlus = has_plus< T, Distance >::value >
struct next_plus_impl;
@@ -107,7 +66,7 @@ struct next_plus_assign_impl< T, Distance, true >
}
};
template< typename T, typename Distance, bool IsIterator = is_iterator< T >::value >
template< typename T, typename Distance, bool IsIterator = boost::iterators::is_iterator< T >::value >
struct next_advance_impl :
public next_plus_assign_impl< T, Distance >
{
@@ -152,7 +111,7 @@ struct prior_minus_assign_impl< T, Distance, true >
}
};
template< typename T, typename Distance, bool IsIterator = is_iterator< T >::value >
template< typename T, typename Distance, bool IsIterator = boost::iterators::is_iterator< T >::value >
struct prior_advance_impl :
public prior_minus_assign_impl< T, Distance >
{