Does the C++ standard guarantee that a failed insertion into an associative container will not modify the rvalue-reference argument?

Question

#include <set>
#include <string>
#include <cassert>

using namespace std::literals;

int main()
{
    auto coll = std::set{ "hello"s };
    auto s = "hello"s;
    coll.insert(std::move(s));
    assert("hello"s == s); // Always OK?
}

Does the C++ standard guarantee that a failed insertion into an associative container will not modify the rvalue-reference argument?

Answer 1

Explicit and unequivocal NO. Standard doesn't have this guarantee, and this is why try_emplace exists.

See notes:

Unlike insert or emplace, these functions do not move from rvalue arguments if the insertion does not happen, which makes it easy to manipulate maps whose values are move-only types, such as std::map<std::string, std::unique_ptr<foo>>. In addition, try_emplace treats the key and the arguments to the mapped_type separately, unlike emplace, which requires the arguments to construct a value_type (that is, a std::pair)