std::ranges::uninitialized_move, std::ranges::uninitialized_move_result

Defined in header `<memory>`
Call signature
template< std::input_iterator I, std::sentinel_for<I> S1, /nothrow-forward-iterator/ O, /nothrow-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 );	(1)	(since C++20) (constexpr since C++26)
template< ranges::input_range IR, /nothrow-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 );	(2)	(since C++20) (constexpr since C++26)
template< /execution-policy/ Ep, std::random_access_iterator I, std::sized_sentinel_for<I> S1, /nothrow-random-access-iterator/ O, /nothrow-sized-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( Ep&& policy, I ifirst, S1 ilast, O ofirst, S2 olast );	(3)	(since C++26)
template< /execution-policy/ Ep, /sized-random-access-range/ IR, /nothrow-sized-random-access-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( Ep&& policy, IR&& in_range, OR&& out_range );	(4)	(since C++26)
Helper types
template< class I, class O > using uninitialized_move_result = ranges::in_out_result<I, O>;	(5)	(since C++20)

For the definition of /*execution-policy*/, see this page; for the definition of /*sized-random-access-range*/, see this page; for the definition of other exposition-only concepts, see this page.

1) Constructs elements in the destination range [ofirst, olast) from elements in the source range [ifirst, ilast) as if by

for(;ifirst!=ilast&&ofirst!=olast;++ofirst,(void)++ifirst) ::new(voidify(*ofirst)) std::remove_reference_t<std::iter_reference_t<O>>(ranges::iter_move(ifirst)); return{std::move(ifirst),ofirst};

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 source range and out_range as the destination range.

3,4) Same as (1,2), but executed according to policy.

The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:

Explicit template argument lists cannot be specified when calling any of them.
None of them are visible to argument-dependent lookup.
When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

Parameters

ifirst, ilast	-	the iterator-sentinel pair defining the input range of elements to move from
in_range	-	the input `range` of elements to move from
ofirst, olast	-	the iterator-sentinel pair defining the output range of elements to initialize
out_range	-	the output `range` to initialize
policy	-	the execution policy to use

Return value

As described above.

Exceptions

Any exception thrown on construction of the elements in the destination range.

3,4) During the execution process:

If the temporary memory resources required for parallelization are not available, std::bad_alloc is thrown.
If an uncaught exception is thrown while accessing objects via an algorithm argument, the behavior is determined by the execution policy (for standard policies, std::terminate is invoked).

Notes

An implementation may improve the efficiency of the ranges::uninitialized_move (by using e.g. ranges::copy) if the value type of the output range is TrivialType.

Feature-test macro	Value	Std	Feature
`__cpp_lib_parallel_algorithm`	`202506L`	(C++26)	Parallel range algorithms
`__cpp_lib_raw_memory_algorithms`	`202411L`	(C++26)	constexpr for specialized `<memory>` algorithms, (1,2)

Possible implementation

struct uninitialized_move_fn
{
    template<std::input_iterator I, std::sentinel_for<I> S1,
             /*nothrow-forward-iterator*/ O, /*nothrow-sentinel-for*/<O> S2>
        requires std::constructible_from<std::iter_value_t<O>,
                                         std::iter_rvalue_reference_t<I>>
    constexpr ranges::uninitialized_move_result<I, O>
        operator()(I ifirst, S1 ilast, O ofirst, S2 olast) const
    {
        using ValueType = std::remove_reference_t<std::iter_reference_t<O>>;
        O current{ofirst};
        try
        {
            for (; !(ifirst == ilast or current == olast); ++ifirst, ++current)
                ::new (static_cast<void*>(std::addressof(*current))))
                    ValueType(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, /*nothrow-forward-range*/ OR>
        requires std::constructible_from<ranges::range_value_t<OR>,
                                         ranges::range_rvalue_reference_t<IR>>
    constexpr 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::next(ranges::begin(out_range), ranges::end(out_range)));
    }
    
    template<ranges::forward_range IR, /*nothrow-forward-range*/ OR>
        requires std::constructible_from<ranges::range_value_t<OR>,
                                         ranges::range_rvalue_reference_t<IR>>
    constexpr 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::next(ranges::begin(in_range), ranges::end(in_range))
                       ranges::begin(out_range),
                       ranges::next(ranges::begin(out_range), ranges::end(out_range)));
    }
};

inline constexpr uninitialized_move_fn uninitialized_move{};

Example

#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);
    }
}

Possible output:

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

ranges::uninitialized_move_n (C++20)	moves a number of objects to an uninitialized area of memory (algorithm function object)
uninitialized_move (C++17)	moves a range of objects to an uninitialized area of memory (function template)