std::uninitialized_move() algorithm

od C++17

// (1)
template< class InputIt, class NoThrowForwardIt >
NoThrowForwardIt uninitialized_move( InputIt first, InputIt last, NoThrowForwardIt d_first );

// (2)
template< class ExecutionPolicy, class ForwardIt, class NoThrowForwardIt >
NoThrowForwardIt uninitialized_move(
  ExecutionPolicy&& policy,
  ForwardIt first,
  ForwardIt last,
  NoThrowForwardIt d_first
);

• (1) Moves elements from the range [first; last) to an uninitialized memory area beginning at d_first as if by:

  for (; first != last; ++d_first, (void) ++first)
      ::new (static_cast<void*>(std::addressof(*d_first)))
          typename std::iterator_traits<NoThrowForwardIt>::value_type(std::move(*first));
  uwaga

  If an exception is thrown during the initialization, some objects in [first; last) are left in a valid but unspecified state, and the objects already constructed are destroyed in an unspecified order.

  Undefined Behaviour

  If d_first + [0, std::distance(first, last)) overlaps with [first, last), the behavior is undefined. (od C++20)

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

Overload Resolution

These overloads participate in overload resolution only if std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>  (do C++20) std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>  (od C++20) is true.

Parameters

first last	The range of the elements to move.
d_first	The beginning of the destination range.
policy	The execution policy to use. See execution policy for details.

Type requirements

InputIt	LegacyInputIterator
ForwardIt NoThrowForwardIt	LegacyForwardIterator

No increment, assignment, comparison, or indirection through valid instances of NoThrowForwardIt may throw exceptions.

Return value

Iterator to the element past the last element moved.

Complexity

Linear in the distance between first and last.

Exceptions

The overloads with a template parameter named ExecutionPolicy report errors as follows:

• If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies, std::terminate is called. For none other ExecutionPolicy, the behavior is implementation-defined.
• If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Possible implementation

uninitialized_move(1)

template<class InputIt, class NoThrowForwardIt>
NoThrowForwardIt uninitialized_move(InputIt first, InputIt last, NoThrowForwardIt d_first)
{
    using Value = typename std::iterator_traits<NoThrowForwardIt>::value_type;
    NoThrowForwardIt current = d_first;
    try
    {
        for (; first != last; ++first, (void) ++current)
            ::new (static_cast<void*>(std::addressof(*current))) Value(std::move(*first));
        return current;
    }
    catch (...)
    {
        std::destroy(d_first, current);
        throw;
    }
}

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", "Work!"};
    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::uninitialized_move(std::begin(in), std::end(in), first);

            print("after move, in: ", std::begin(in), std::end(in));
            print("after move, out: ", first, last);

            std::destroy(first, last);
        }
        catch (...)
        {
            std::cout << "Exception!\n";
        }
        std::free(out);
    }
}

Output

initially, in: "Home" "Work!"
after move, in: "" ""
after move, out: "Home" "Work!"