C++20 std::move 在自赋值中

Question

Most answers, including this one, point out that std::move is not meant to be used in self-assignment.
I do, however, see the Possible Implementation of accumulate in official reference via self move assignment:

template<class InputIt, class T>
constexpr // since C++20
T accumulate(InputIt first, InputIt last, T init)
{
    for (; first != last; ++first) {
        init = std::move(init) + *first; // std::move since C++20
    }
return init;
}

Is it safe only since C++20? What is happening internally?
The EXP63-CPP states that:

it should be assumed that the only operations that may be safely performed on a moved-from object instance are reinitialization through assignment into the object or terminating the lifetime of the object by invoking its destructor

Looks like reinitialization is completely legal.

Answer 1

This is not a self-assignment.

A self-assignment would be init = std::move(init); , and you have init = std::move(init) + *first; .