std::ranges::uninitialized_move() algorithm

od C++20

Simplified

// (1)uninitialized_move_result<I, O>  uninitialized_move( I ifirst, S1 ilast, O ofirst, S2 olast );// (2)uninitialized_move_result< ranges::borrowed_iterator_t<IR>,                           ranges::borrowed_iterator_t<OR> >  uninitialized_move( IR&& in_range, OR&& out_range );

The type of arguments are generic and have following constraints:

• I - std::input_iterator
• S1 - std::sentinel_for<I>, no-throw-sentinel-for<O>
• O - no-throw-forward-iterator
• IR - ranges::input_range
• OR - no-throw-forward-range

Additionally, each overload has the following constraints:

• (1) std::constructible_from< std::iter_value_t<O>, std::iter_rvalue_reference_t<I> >
• (1) std::constructible_from< ranges::range_value_t<OR>, ranges::range_rvalue_reference_t<IR> >

Detailed

// (1)template<  std::input_iterator I,  std::sentinel_for<I> S1,  no-throw-forward-iterator O,  no-throw-sentinel-for<O> S2>  requires std::constructible_from< std::iter_value_t<O>,                                    std::iter_rvalue_reference_t<I> >uninitialized_move_result<I, O>  uninitialized_move( I ifirst, S1 ilast, O ofirst, S2 olast );// (2)template<  ranges::input_range IR,  no-throw-forward-range OR>  requires std::constructible_from< ranges::range_value_t<OR>,                                    ranges::range_rvalue_reference_t<IR> >uninitialized_move_result< ranges::borrowed_iterator_t<IR>,                           ranges::borrowed_iterator_t<OR> >  uninitialized_move( IR&& in_range, OR&& out_range );

With the helper types defined as follows:

template< class I, class O >using uninitialized_move_result = ranges::in_out_result<I, O>;

• (1) Moves N elements from the input range [ifirst; ilast) to the output range [ofirst; olast), where N is min(ranges::distance(ifirst, ilast), ranges::distance(ofirst, olast)).

  The function has the effect equal to:

  for (; ifirst != ilast && ofirst != olast; ++ofirst, ++ifirst)    ::new (static_cast<void*>(std::addressof(*first)))        std::remove_reference_t<std::iter_reference_t<O>>(ranges::iter_move(ifirst));
  uwaga

  If an exception is thrown during the initialization then the objects that already constructed in [ofirst; olast) are destroyed in an unspecified order.

  Also, the objects in [ifirst; ilast) that were already moved, are left in a valid but unspecified state.

• (2) Same as (1), but uses in_range as the first range and out_range as the second range, as if using ranges::begin(in_range) as ifirst, ranges::end(in_range) as ilast, ranges::begin(out_range) as ofirst, and ranges::end(out_range) as olast.

The function-like entities described on this page are niebloids.

Parameters

ifirst ilast	The input range to move elements from.
in_range	The input range to move elements from.
ofirst olast	The destination range to initialize.
out_range	The destination range to initialize.

Return value

{  ifirst + N,  ofirst + N}

Complexity

Linear in N.

Exceptions

The exception thrown on construction of the elements in the destination range, if any.

Possible implementation

uninitialized_move(1) and uninitialized_move(2)

struct uninitialized_move_fn{    template<std::input_iterator I, std::sentinel_for<I> S1,             no-throw-forward-iterator O, no-throw-sentinel-for<O> S2>    requires std::constructible_from<std::iter_value_t<O>,             std::iter_rvalue_reference_t<I>>    ranges::uninitialized_move_result<I, O>    operator()(I ifirst, S1 ilast, O ofirst, S2 olast) const    {        O current{ofirst};        try        {            for (; !(ifirst == ilast or current == olast); ++ifirst, ++current)                ::new (const_cast<void*>(static_cast<const volatile void*>                    (std::addressof(*current)))) std::remove_reference_t<                        std::iter_reference_t<O>>(ranges::iter_move(ifirst));            return {std::move(ifirst), std::move(current)};        }        catch (...) // rollback: destroy constructed elements        {            for (; ofirst != current; ++ofirst)                ranges::destroy_at(std::addressof(*ofirst));            throw;        }    }    template<ranges::input_range IR, no-throw-forward-range OR>    requires std::constructible_from<ranges::range_value_t<OR>,             ranges::range_rvalue_reference_t<IR>>    ranges::uninitialized_move_result<ranges::borrowed_iterator_t<IR>,             ranges::borrowed_iterator_t<OR>>    operator()(IR&& in_range, OR&& out_range) const    {        return (*this)(ranges::begin(in_range), ranges::end(in_range),                       ranges::begin(out_range), ranges::end(out_range));    }};inline constexpr uninitialized_move_fn uninitialized_move{};

Notes

An implementation may improve the efficiency of ranges::uninitialized_move if the value type of the output range is TrivialType.

Examples

Main.cpp

#include <cstdlib>#include <iomanip>#include <iostream>#include <memory>#include <string>void print(auto rem, auto first, auto last){    for (std::cout << rem; first != last; ++first)        std::cout << std::quoted(*first) << ' ';    std::cout << '\n';}int main(){    std::string in[]{"Home", "World"};    print("initially, in: ", std::begin(in), std::end(in));    if (        constexpr auto sz = std::size(in);        void* out = std::aligned_alloc(alignof(std::string), sizeof(std::string) * sz)    )    {        try        {            auto first{static_cast<std::string*>(out)};            auto last{first + sz};            std::ranges::uninitialized_move(std::begin(in), std::end(in), first, last);            print("after move, in: ", std::begin(in), std::end(in));            print("after move, out: ", first, last);            std::ranges::destroy(first, last);        }        catch (...)        {            std::cout << "Exception!\n";        }        std::free(out);    }}

Output

initially, in: "Home" "World"after move, in: "" ""after move, out: "Home" "World"