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

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C++
Utilities library
General utilities
Relational operators (deprecated in C++20)
Dynamic memory management
Uninitialized memory algorithms
Constrained uninitialized memory algorithms
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Garbage collection support
(C++11) (until C++23)
(C++11) (until C++23)
(C++11) (until C++23)
(C++11) (until C++23)
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Defined in header <memory>
Call signature
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 ) ;
(1) (since C++20)
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 ) ;
(2) (since C++20)
Helper types
template < class I, class O >
using uninitialized_move_result = ranges:: in_out_result < I, O > ;
(3) (since C++20)
1) Moves N elements from the input range [ ifirst , ilast ) to the output range [ ofirst , olast ) (that is an uninitialized memory area), where N is min ( ranges:: distance ( ifirst, ilast ) , ranges:: distance ( ofirst, olast ) ) .
The effect is equivalent to: 
for (; ifirst != ilast && ofirst != olast; ++ofirst, ++ifirst)
    ::new (static_cast<void*>(std::addressof(*ofirst)))
        std::remove_reference_t<std::iter_reference_t<O>>(ranges::iter_move(ifirst));
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 algorithm function objects (informally known as niebloids ), that is:

Parameters

ifirst, ilast - iterator-sentinel pair denoting the input range of elements to move from
in_range - the input range of elements to move from
ofirst, olast - iterator-sentinel pair denoting the output range to initialize
out_range - the output 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.

Notes

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

Possible implementation 

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{};

Example

Run this code 
#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"

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 3870 C++20 this algorithm might create objects on a const storage kept disallowed

See also

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