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1029. Specialized algorithms for memory management need to be concept-constrained templates

Section: 26.11 [specialized.algorithms] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

Addresses UK 210 [CD1]

Related to 582⁽ⁱ⁾

Specialized algorithms for memory management need requirements to be easily usable in constrained templates.

[ Summit: ]

We look forward to a paper on this topic. We recommend no action until a paper is available.

[ Post Summit Alisdair provided wording. ]

[ Post Summit: ]

Daniel adds:

1. I suggest Size should require IntegralLike and not UnsignedIntegralLike, because otherwise simple int-literals could not be provided as arguments and it would conflict with other algorithms that only require IntegralLike.

2. The current for-loop-test relies on evaluation in boolean context which is not provided by ArithmeticLike and it's refinements. I propose to change the corresponding for-loop-headers to:

   1. for uninitialized_copy_n: for ( ; n > Size(0); ++result, ++first, --n) {
   2. for uninitialized_fill_n: for (; n > Size(0); ++first, --n) {

Alisdair adds:

For the record I agree with Daniel's suggestion.

Proposed resolution:

20.2 [memory] p2

Update the synopsis for <memory>

template <class InputIterator InIter,
         class ForwardIterator OutputIterator<auto, InIter::reference> OutIter> 
   requires ForwardIterator<OutIter>
   ForwardIterator OutIter
   uninitialized_copy(InputIterator InIter first, InputIterator InIter last, 
                      ForwardIterator OutIter result);

template <class InputIterator InIter,
          class IntegralLike Size,
          class ForwardIterator OutputIterator<auto, InIter::reference> OutIter> 
  requires ForwardIterator<OutIter>
  ForwardIterator OutIter
  uninitialized_copy_n(InputIterator InIter first, Size n, 
                       ForwardIterator OutIter result);

template <class ForwardIterator Iter, class ObjectType T>
  requires Constructible< Iter::value_type, const T& >
  void uninitialized_fill(ForwardIterator Iter first, ForwardIterator Iter last, 
                          const T& x);

template <class ForwardIterator Iter, class IntegralLike Size, class ObjectType T> 
  requires Constructible< Iter::value_type, const T& >
  void
  uninitialized_fill_n(ForwardIterator Iter first, Size n, const T& x);

Update as follows:

uninitialized_copy 26.11.5 [uninitialized.copy]

template <class InputIterator InIter,
         class ForwardIterator OutputIterator<auto, InIter::reference> OutIter> 
   requires ForwardIterator<OutIter>
   ForwardIterator OutIter
   uninitialized_copy(InputIterator InIter first, InputIterator InIter last, 
                      ForwardIterator OutIter result);

-1- Effects:

for (; first != last; ++result, ++first)  {
   new (static_cast<void*>(&*result))
       typename iterator_traits<ForwardIterator> OutIter::value_type(*first);
}

-2- Returns: result

template <class InputIterator InIter,
          class IntegralLike Size,
          class ForwardIterator OutputIterator<auto, InIter::reference> OutIter> 
  requires ForwardIterator<OutIter>
  ForwardIterator OutIter
  uninitialized_copy_n(InputIterator InIter first, Size n, 
                       ForwardIterator OutIter result);

-3- Effects:

for ( ; n > Size(0); ++result, ++first, --n) {
   new (static_cast<void*>(&*result))
       typename iterator_traits<ForwardIterator> OutIter::value_type(*first);
}

-4- Returns: result

uninitialized_fill 26.11.7 [uninitialized.fill]

template <class ForwardIterator Iter, class ObjectType T>
  requires Constructible< Iter::value_type, const T& >
  void uninitialized_fill(ForwardIterator Iter first, ForwardIterator Iter last, 
                          const T& x);

-1- Effects:

for (; first != last; ++first) {
   new ( static_cast<void*>( &*first) ) 
       typename iterator_traits<ForwardIterator> Iter::value_type(x);
}

uninitialized_fill_n [uninitialized.fill.n]

template <class ForwardIterator Iter, class IntegralLike Size, class ObjectType T> 
  requires Constructible< Iter::value_type, const T& >
  void
  uninitialized_fill_n(ForwardIterator Iter first, Size n, const T& x);

-1- Effects:

for (; n-- > Size(0); ++first, --n) {
   new ( static_cast<void*>( &*first) ) 
       typename iterator_traits<ForwardIterator> Iter::value_type(x);
}