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

Let \(\scriptsize N\)N be ranges::min (ranges::distance (ifirst, ilast), ranges::distance (ofirst, olast)).

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.

[edit] Parameters

[edit] Return value

As described above.

[edit] Complexity

Linear in \(\scriptsize N\)N.

[edit] Exceptions

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

[edit] 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.

[edit] 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>>
 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, no-throw-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::end (out_range));
 }
};
 
inline constexpr uninitialized_move_fn uninitialized_move{};

[edit] 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);
 }
}

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

[edit] Defect reports

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

[edit] See also

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