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Gather does not (in general) work with forward iterators, even though it does on some systems

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[SVN r83158]
This commit is contained in:
Marshall Clow
2013-02-25 22:31:52 +00:00
parent 5f45246c6c
commit ef16153353
3 changed files with 18 additions and 19 deletions
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16
doc/gather.qbk
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@ -22,13 +22,13 @@ There are two versions; one takes two iterators, and the other takes a range.
`` ``
namespace boost { namespace algorithm { namespace boost { namespace algorithm {
template <typename ForwardIterator, typename Pred> template <typename BidirectionalIterator, typename Pred>
std::pair<ForwardIterator,ForwardIterator> std::pair<BidirectionalIterator,BidirectionalIterator>
gather ( ForwardIterator first, ForwardIterator last, ForwardIterator pivot, Pred pred ); gather ( BidirectionalIterator first, BidirectionalIterator last, BidirectionalIterator pivot, Pred pred );
template <typename ForwardRange, typename Pred> template <typename BidirectionalRange, typename Pred>
std::pair<typename boost::range_iterator<ForwardRange>::type, typename boost::range_iterator<ForwardRange>::type> std::pair<typename boost::range_iterator<const BidirectionalRange>::type, typename boost::range_iterator<const BidirectionalRange>::type>
gather ( ForwardRange &range, typename boost::range_iterator<ForwardRange>::type pivot, Pred pred ); gather ( const BidirectionalRange &range, typename boost::range_iterator<const BidirectionalRange>::type pivot, Pred pred );
}} }}
`` ``
@ -53,11 +53,11 @@ where `first` and `second` are the fields of the pair that is returned by the ca
[heading Iterator Requirements] [heading Iterator Requirements]
`gather` work on all iterators except input or output iterators. `gather` work on bidirectional iterators or better. This requirement comes from the usage of `stable_partition`, which requires bidirectional iterators. Some standard libraries (libstdc++ and libc++, for example) have implementations of `stable_partition` that work with forward iterators. If that is the case, then `gather` will work with forward iterators as well.
[heading Storage Requirements] [heading Storage Requirements]
`gather` uses stable_partition, which will attempt to allocate temporary memory, but will work in-situ if there is none available. `gather` uses `stable_partition`, which will attempt to allocate temporary memory, but will work in-situ if there is none available.
[heading Complexity] [heading Complexity]

17
include/boost/algorithm/gather.hpp
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@ -80,9 +80,10 @@ namespace boost { namespace algorithm {
*/ */
template < template <
typename ForwardIterator, // Iter models ForwardIterator typename BidirectionalIterator, // Iter models BidirectionalIterator
typename Pred> // Pred models UnaryPredicate typename Pred> // Pred models UnaryPredicate
std::pair<ForwardIterator,ForwardIterator> gather ( ForwardIterator first, ForwardIterator last, ForwardIterator pivot, Pred pred ) std::pair<BidirectionalIterator, BidirectionalIterator> gather
( BidirectionalIterator first, BidirectionalIterator last, BidirectionalIterator pivot, Pred pred )
{ {
// The first call partitions everything up to (but not including) the pivot element, // The first call partitions everything up to (but not including) the pivot element,
// while the second call partitions the rest of the sequence. // while the second call partitions the rest of the sequence.
@ -99,14 +100,14 @@ std::pair<ForwardIterator,ForwardIterator> gather ( ForwardIterator first, Forwa
*/ */
template < template <
typename ForwardRange, // typename BidirectionalRange, //
typename Pred> // Pred models UnaryPredicate typename Pred> // Pred models UnaryPredicate
std::pair< std::pair<
typename boost::range_iterator<ForwardRange>::type, typename boost::range_iterator<const BidirectionalRange>::type,
typename boost::range_iterator<ForwardRange>::type> typename boost::range_iterator<const BidirectionalRange>::type>
gather ( gather (
ForwardRange &range, const BidirectionalRange &range,
typename boost::range_iterator<ForwardRange>::type pivot, typename boost::range_iterator<const BidirectionalRange>::type pivot,
Pred pred ) Pred pred )
{ {
return boost::algorithm::gather ( boost::begin ( range ), boost::end ( range ), pivot, pred ); return boost::algorithm::gather ( boost::begin ( range ), boost::end ( range ), pivot, pred );

4
test/gather_test1.cpp
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@ -55,14 +55,12 @@ void test_iterators ( Iterator first, Iterator last, Predicate comp, std::size_t
template <typename Container, typename Predicate> template <typename Container, typename Predicate>
void test_iterator_types ( const Container &c, Predicate comp, std::size_t offset ) { void test_iterator_types ( const Container &c, Predicate comp, std::size_t offset ) {
typedef std::vector<typename Container::value_type> vec; typedef std::vector<typename Container::value_type> vec;
typedef forward_iterator<typename vec::iterator> FI;
typedef bidirectional_iterator<typename vec::iterator> BDI; typedef bidirectional_iterator<typename vec::iterator> BDI;
typedef random_access_iterator<typename vec::iterator> RAI; typedef random_access_iterator<typename vec::iterator> RAI;
vec v; vec v;
v.assign ( c.begin (), c.end ()); v.assign ( c.begin (), c.end ());
test_iterators ( FI ( v.begin ()), FI ( v.end ()), comp, offset );
v.assign ( c.begin (), c.end ());
test_iterators ( BDI ( v.begin ()), BDI ( v.end ()), comp, offset ); test_iterators ( BDI ( v.begin ()), BDI ( v.end ()), comp, offset );
v.assign ( c.begin (), c.end ()); v.assign ( c.begin (), c.end ());
test_iterators ( RAI ( v.begin ()), RAI ( v.end ()), comp, offset ); test_iterators ( RAI ( v.begin ()), RAI ( v.end ()), comp, offset );